Feedback loop for controlling a pulsed voltage waveform

ABSTRACT

Embodiments of this disclosure describe a feedback loop that can be used to maintain a nearly constant sheath voltage and thus creating a mono-energetic IEDF at the surface of the substrate. The system described herein consequently enables a precise control over the shape of IEDF and the profile of the features formed in the surface of the substrate.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional patent application Ser. No. 62/795,545, filed Jan. 22, 2019, which is hereby incorporated herein by reference.

BACKGROUND Field

Embodiments described herein generally relate to plasma processing chambers used in semiconductor manufacturing, and more specifically to an apparatus and methods of controlling the delivery of power to a plasma formed in plasma processing chamber.

Description of the Related Art

Reliably producing high aspect ratio features is one of the key technology challenges for the next generation of very large scale integration (VLSI) and ultra large scale integration (ULSI) of semiconductor devices. One method of forming high aspect ratio features uses a plasma assisted etching process, such as a reactive ion etch (RIE) plasma process, to form high aspect ratio openings in a material layer, such as a dielectric layer, of a substrate. In a typical RIE plasma process, a plasma is formed in an RIE processing chamber and ions from the plasma are accelerated towards a surface of a substrate to form openings in a material layer disposed beneath a mask layer formed on the surface of the substrate.

A typical Reactive Ion Etch (RIE) plasma processing chamber includes a radio frequency (RF) bias generator, which supplies an RF voltage to a “power electrode” (e.g., a biasing electrode), such as a metal baseplate embedded into an “electrostatic chuck” (ESC) assembly, more commonly referred to as the “cathode”. The power electrode is capacitively coupled to the plasma of a processing system through a thick layer of dielectric material (e.g., ceramic material), which is a part of the ESC assembly. The application of RF voltage to the power electrode causes an electron-repelling plasma sheath (also referred to as the “cathode sheath”) to form over a processing surface of a substrate that is positioned on a substrate supporting surface of the ESC assembly during processing. The non-linear, diode-like nature of the plasma sheath results in rectification of the applied RF field, such that a direct-current (DC) voltage drop, or “self-bias”, appears between the substrate and the plasma, making the substrate potential negative with respect to the plasma potential. This voltage drop determines the average energy of the plasma ions accelerated towards the substrate, and thus etch anisotropy. More specifically, ion directionality, the feature profile, and etch selectivity to the mask and the stop-layer are controlled by the Ion Energy Distribution Function (IEDF). In plasmas with RF bias, the IEDF typically has two peaks, one at a low energy and one at a high energy, and some ion population in between. The presence of the ion population in-between the two peaks of the IEDF is reflective of the fact that the voltage drop between the substrate and the plasma oscillates at the RF bias frequency. When a lower frequency, e.g., 2 MHz, RF bias generator is used to achieve higher self-bias voltages, the difference in energy between these two peaks can be significant; and because the etch profile due to the ions at low energy peak is more isotropic, this could potentially lead to bowing of the etched feature walls. Compared to the high-energy ions, the low-energy ions are less effective at reaching the corners at the bottom of the etched feature (e.g., due to the charging effect), but cause less sputtering of the mask material. This is important in high aspect ratio etch applications, such as hard-mask opening or dielectric mold etch. As feature sizes continue to diminish and the aspect ratio increases, while feature profile control requirements become more stringent, it becomes more desirable to have a well-controlled IEDF at the substrate surface during processing.

A pulsed voltage waveform generator (PVWG) may be used to create a pulsed voltage waveform at an electrode embedded in the electrostatic chuck (ESC) assembly in a semiconductor plasma chamber in order to maintain a particular substrate voltage waveform, and thus control the sheath voltage and the IEDF at the substrate during plasma processing. A difficulty in controlling the produced waveform may arise from real-time changes in the load, such as drifts in the plasma density, chamber walls conditions, substrate temperature, degree and state of chemical dissociation, in the case of a semiconductor plasma chamber used as a load. Therefore, a real-time information about the waveform can be very helpful in order to perform real-time adjustments to the PVWG control parameters (e.g., a charge voltage of DC power supplies or a pulse width controlled by the arbitrary waveform generator) and thus maintain a predetermined voltage waveform despite the changes in the load. Such real-time measurements and analysis performed together with real-time control is often referred to as “closed feedback loop operation”. However, certain difficulties arise in measurements and analysis of a pulsed voltage waveform due to its very high amplitude (e.g. several to tens of kV, as is often the case in plasma processing), as well as due to the complex nature of a load, such as a semiconductor plasma chamber. When PVWG is connected to a complex load, which may include a series and/or parallel combination of discrete capacitive, inductive, resistive and nonlinear elements (e.g., plasma sheath at the substrate surface in a process chamber) as well as the distributed elements (e.g., a section of a transmission line), the produced waveform may have a much more complex structure than a theoretically predicted (expected) waveform and may include high frequency oscillations, which can affect the ability to repeatably control a plasma process.

Accordingly, there is a need in the art for novel biasing methods that enable maintaining a nearly constant sheath voltage, and thus create a desirable and repeatable mono-energetic IEDF at the surface of the substrate to enable a precise control over the shape of IEDF and the profile of the features formed in the surface of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments and are therefore not to be considered limiting of its scope, and may admit to other equally effective embodiments.

FIG. 1A is a schematic diagram of a feedback loop that is configured to be attached to a plasma processing chamber, according to one embodiment.

FIG. 1B is a schematic diagram illustrating an example of the feedback loop illustrated in FIG. 1A, according to one embodiment.

FIG. 1C is a schematic diagram illustrating an example of the feedback loop illustrated in FIG. 1A, according to one embodiment.

FIG. 1D is a schematic diagram illustrating an example of the feedback loop illustrated in FIG. 1A, according to one embodiment.

FIG. 2 is a schematic illustration of a voltage divider that can be disposed within a feedback loop, according to one or more embodiments.

FIG. 3 s a schematic illustration of a low pass filter that can be disposed within a feedback loop, according to one or more embodiments.

FIG. 4 illustrates a frequency response curve of the low pass filter illustrated in FIG. 3, according to one embodiment.

FIGS. 5A, 5B, 5C and 5D illustrate examples of conditioned voltage waveforms generated by components within the feedback loop, according to one or more embodiment.

FIGS. 6A and 6B illustrate examples of different types of measured voltage waveforms, according to one embodiment.

FIG. 7A illustrates an example of a series of measured voltage waveforms, according to one or more embodiments.

FIG. 7B illustrates an example of a series of measured voltage waveform bursts, according to one or more embodiments.

FIG. 8A is a schematic cross-sectional view of a processing chamber configured to practice methods described herein, according to one embodiment.

FIG. 8B is a functionally equivalent approximate circuit diagram of a pulsed voltage biasing scheme that can be used with the process chamber illustrated in FIG. 8A, according to one embodiment.

FIG. 9A illustrates an example of a pulsed voltage waveform established at the biasing electrode, according to one embodiment.

FIG. 9B illustrates an example of a pulsed voltage waveform established at a substrate, according to one embodiment.

FIG. 9C illustrates an example of a single-peak IEDF, according to one embodiment.

FIG. 10 is a flow diagram of a method of processing a substrate using a pulsed voltage biasing scheme described herein, according to one embodiment.

FIG. 11 is a flow diagram of a method of processing a substrate using a pulsed voltage biasing scheme described herein, according to one embodiment.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

SUMMARY

Embodiments of the disclosure provided herein may include a feedback loop for controlling a pulsed voltage waveform comprising a data acquisition system comprising a first input channel comprising a first conditioning circuit configured to generate a first conditioned voltage waveform from a first input voltage waveform, and a fast data acquisition module. The fast data acquisition module may include a first acquisition channel that is electrically coupled to the first conditioning circuit of the first input channel, and is configured to generate a first digitized voltage waveform from the first conditioned voltage waveform, and a data acquisition controller configured to determine one or more one-cycle waveform characteristics of the first conditioned voltage waveform by analyzing the first digitized voltage waveform. The feedback loop may further include a feedback processor configured to process the information related to the first conditioned voltage waveform processed by the fast data acquisition module. In some embodiments, the pulsed voltage waveform is established by a pulsed voltage waveform generator that is electrically coupled to a biasing electrode disposed within a substrate support assembly disposed within a plasma processing chamber.

Embodiments of the disclosure provided herein may also include a feedback loop for controlling a pulsed voltage waveform comprising a data acquisition system comprising a first input channel comprising a first conditioning circuit configured to generate a first conditioned voltage waveform from a first input voltage waveform, a second input channel comprising a second conditioning circuit configured to generate a second conditioned voltage waveform from a second input voltage waveform; and a fast data acquisition module. The fast data acquisition module may include a first acquisition channel that is electrically coupled to the first conditioning circuit of the first input channel, and is configured to generate a first digitized voltage waveform from the first conditioned voltage waveform, a second acquisition channel that is electrically coupled to the second conditioning circuit of the second input channel, and is configured to generate a second digitized voltage waveform from the second conditioned voltage waveform, and a data acquisition controller configured to determine one or more one-cycle waveform characteristics of at least one of the first and the second conditioned voltage waveforms by analyzing at least one of the first and the second digitized voltage waveforms. In some embodiments, the pulsed voltage waveform is established by a pulsed voltage waveform generator that is electrically coupled to a biasing electrode disposed within a substrate support assembly disposed within a plasma processing chamber. In some embodiments, the pulsed voltage waveform generator is also electrically coupled to the biasing electrode through an electrical conductor using a generator coupling assembly, and wherein the input end of the first input channel is electrically coupled to an end of the generator coupling assembly, and the input end of the second input channel is electrically coupled to one of an output of a current monitor and a non-grounded end of the current sense resistor, wherein the current monitor is configured to sense a current flowing in the electrical conductor and the current sense resistor is placed within a pulsed voltage waveform generator.

DETAILED DESCRIPTION

Embodiments of the disclosure provided herein include a closed feedback loop scheme that is suitable for operation with a pulsed voltage waveform generator to produce controlled and repeatable pulsed voltage waveforms. Embodiments described herein can thus be used in many different types of plasma assisted or plasma enhanced processing chambers that are used to perform plasma assisted or plasma enhanced processing of a substrate. While not intending to be limiting as to the scope of the disclosure provided herein, in some embodiments, a pulsed voltage biasing scheme is used during plasma processing to maintain a nearly constant sheath voltage for up to about 90% of the substrate processing time, which results in a single (narrow) peak IEDF that can be further used to create an IEDF with an arbitrary shape. Further, in one or more of the embodiments disclosed herein, a plasma processing method includes a pulsed voltage waveform that further includes multiple cycles, such as, for example, a periodic series of short positive pulses repeating with a period Ts (e.g., 2.5 microseconds), wherein the overall period Tp of each pulse is typically on the order of several tens of nanoseconds (e.g., 10-100 ns), and each cycle of the multiple cycles corresponds to one or more pulses.

FIG. 1A schematically illustrates a feedback loop 100 that is electrically coupled to one or more electrical components found in a plasma processing system 50. In general, the feedback loop 100 includes one or more input channels 110 and a fast data acquisition module 120. The one or more input channels 110 are electrically coupled to a fast data acquisition module 120. In some embodiments, the fast data acquisition module 120 is configured to control and maintain a generated pulsed voltage waveform, such as a high voltage nanosecond substrate voltage waveform, to control the sheath voltage and the IEDF at the substrate during plasma processing. Further, the fast data acquisition module 120 includes one or more acquisition channels 122.

An input end of one or more input channels 110 is coupled to a connection point 135 within the plasma processing system 50. Accordingly, an input pulsed voltage waveform 140, which is received and then conditioned by one or more input channels 110, can then be processed by components in the fast data acquisition module 120 and components within a feedback processor 125 so that control parameters can be provided to a pulsed waveform generator (e.g., the pulsed voltage waveform generator (PVWG) 150 of FIG. 1B) within the plasma processing system 50, to control the characteristics of a pulsed voltage waveform established at an electrode (e.g., biasing electrode disposed within a substrate support) positioned within a processing chamber of the plasma processing system 50. The one or more input channels 110 receive the input pulsed voltage waveform 140 and generate an output waveform 144 from the input pulsed voltage waveform 140. As will be described in more detail in the following description, the input pulsed voltage waveform 140 may be processed by the input channel 110 to generate the output waveform 144 that comprises a conditioned waveform. For example, the input channel 110 may condition the received input pulsed voltage waveform 140, via a conditioning circuit to generate the output waveform 144. Accordingly, for example, the amplitude and/or shape of the output waveform 144 may differ from that of the input pulsed voltage waveform 140. One will note that the characteristics of a pulsed voltage waveform received by an input channel 110 (i.e., input pulsed voltage waveform 140) can have different characteristics depending on the position of the connection point 135 relative to inductive, capacitive or resistive elements formed and/or positioned within one or more circuits coupled to the complex load 130 (FIG. 1B) of the plasma processing system 50. In some embodiments, the input channels 110 within the feedback loop 100 may each have different degrees of attenuation of the incoming signal due to differences in the types of components (e.g., voltage dividing components or filtering components) found within each of the input channels. Therefore, input channels 110 may be referred to herein as channels having a high-attenuation, a mid-attenuation, or low-attenuation, or be unattenuated, based on their degree of attenuation or conditioning of the received input pulsed voltage waveform 140.

FIG. 1B schematically illustrates an example of the feedback loop 100 shown in FIG. 1A which includes multiple input channels 110 that are each electrically coupled to corresponding acquisition channels 122 of the fast data acquisition module 120. As shown in FIG. 1B, an input channel 110 can be coupled to a connection point that is coupled to a conductive element positioned on either side of a generator coupling assembly 133, which are all used in combination to connect the output of the PVWG 150 to the complex load 130. In general, the conductive elements and generator coupling assembly 133, which are used to connect the output of the PVWG 150 to the complex load 130, are often referred to herein as being elements within a transmission line 131. Thus, the PVWG 150 is electrically connected to the complex load 130 via the transmission line 131 and a reference line 132. In general, the term “electrical conductor” or “conductor” as used herein may include: (a) a coaxial transmission line, which may include a flexible coaxial cable in series with a rigid coaxial transmission line, (b) an insulated high-voltage corona-resistant hookup wire, (c) a bare wire, (d) a metal rod, (e) an electrical connector, or (f) any combination of electrical elements in (a)-(e). While FIG. 1B schematically illustrates a configuration in which multiple input channels 110 are coupled to a connection point that is coupled to one of one or more conductive elements that are used to connect the output of the PVWG 150 to the complex load 130 and/or one or more circuits within the PVWG 150, this configuration is not intended to be limiting as to the scope of the disclosure provided herein since the number of input channels 110 and/or the number of different positions that the various input channels 110 could be connected to within the plasma processing system 50 could be increased or decreased as required to control a desired chamber processing application.

As illustrated in FIG. 1B, the plasma processing system 50 includes a pulsed voltage waveform generator (PVWG), such as the PVWG 150 of the processing chamber 800 schematically illustrated in FIGS. 8A and 8B. Further, the plasma processing system 50 includes a complex load 130, which includes and/or is formed by generating a pulsed voltage waveform at a biasing electrode (e.g., a biasing electrode 804 in FIG. 8A) during plasma processing. The feedback loop 100 is generally configured to control the pulsed voltage waveform by adjusting one or more characteristics of the generated pulsed voltage waveform generated by the PVWG 150.

One or more of the input channels 110 can include a conditioning circuit 111, such as, for example, a conditioning circuit 111 ₁ in input channel 110 ₁ and a conditioning circuit 111 ₂ in input channel 110 ₂. Further, the one or more input channels 110 are configured to generate output waveforms 144 that are conditioned. In some embodiments, the conditioning circuits 111 may each include a voltage divider (e.g., the voltage divider 112 of FIG. 2), a low pass filters 114 (e.g., the low pass filter of FIG. 3), both a voltage divider and a low pass filters 114, or even in some cases neither a voltage divider nor a low pass filters 114 which is referred to herein as an unattenuated conditioning circuit. In one example, a feedback loop 100 includes at least three conditioning circuits 111 in which one conditioning circuit includes a high-ratio voltage divider, another conditioning circuit includes a mid-ratio voltage divider, and the other conditioning circuit includes only a filter, and thus does not contain a voltage divider. In embodiments where the conditioning circuits 111 of the input channel 110 includes a voltage divider and also a low pass filter, the voltage divider 112 is electrically coupled to the low pass filter 114. Further, in such embodiments, the voltage divider generates a divided voltage waveform from an input pulsed voltage waveform 140 and the low pass filter generates a filtered voltage waveform from the divided voltage waveform. In embodiments where the low pass filter is omitted, the voltage divider generates a divided voltage waveform from the input pulsed voltage waveform 140, and the divided voltage waveform is communicated to the fast data acquisition module 120. In such embodiments, the divided voltage waveform is a conditioned voltage waveform, which is the output waveform 144. In embodiments where the voltage divider and the low pass filter are both omitted from the input channel 110, the input pulsed voltage waveform 140 is also the output waveform 144. In embodiments where the voltage divider is omitted and a low pass filter is present in the conditioning circuits 111, the low pass filter generates a filtered voltage waveform from the input pulsed voltage waveform 140, and the filtered waveform is communicated to the fast data acquisition module 120.

FIG. 1B illustrates the input channels 110 ₁-110 _(N), where N is generally a number greater than one, such as a number greater than three, as shown in FIG. 1B. Each of the input channels 110 ₁-110 _(N) may be connected to different points within the plasma processing system 50. For example, the input channel 110 ₁ may be connected to an electrical conductor positioned on either side of a generator coupling assembly 133, which may include a blocking capacitor (e.g., capacitor C_(hvm) of FIG. 8B). For example, the input channel 110 ₁ is coupled between the complex load 130 and the generator coupling assembly 133, or the input channel 110 ₁ is coupled between the output of the PVWG 150 and the generator coupling assembly 133. In embodiments where the input channel 110 ₁ is coupled between the output of the PVWG 150 and the generator coupling assembly 133, the input channel 110 ₁ receives the input pulsed voltage waveform 140 _(1A) and the conditioning circuit 111 ₁ generates the output waveform (e.g., a conditioned waveform) 144 _(1A). In one example, a received or measured input pulsed voltage waveform 140 _(1A) includes voltage pulses that include positive and negative voltage levels within different phases of each of the voltage pulses (i.e., pulses are above and below the dashed zero volt reference line) and high frequency oscillations within various phases of a pulse within the input pulsed voltage waveform 140 _(1A) (e.g., see the dashed circle highlighting a region of a pulse), which when conditioned by the components, such as a voltage divider, within the conditioning circuit 111 _(1A) forms an output waveform 144 _(1A) that is at least provided at a lower voltage level due to the use of a voltage divider. In embodiments where the input channel 110 ₁ is coupled between the complex load 130 and the generator coupling assembly 133, the input channel 110 ₁ receives the input pulsed voltage waveform 140 _(1B) and the conditioning circuit 111 ₁ generates the output waveform (e.g., a conditioned waveform) 144 _(1B). As is illustrated in FIG. 1B, input pulsed voltage waveform 140 _(1A) has different waveform characteristics from the input pulsed voltage waveform 140 _(1B) due to the position of their respective connection points along the transmission line 131 within the plasma processing system 50. Alternately, in one example, as shown in FIG. 1B, a received or measured input pulsed voltage waveform 140 _(1B) includes positive voltage pulses (i.e., pulses are above the dashed zero volt reference line) that include high frequency oscillations within a phase of a pulse within the input pulsed voltage waveform 140 _(1B) (e.g., pulse region I_(1B)), which when conditioned by the components, such as a voltage divider and a low pass filter found within the conditioning circuit 111 _(1B), to form an output waveform 144 _(1B) that is a filtered waveform that is at a reduced voltage level.

With further reference to FIG. 1B, the input channel 110 ₂ is connected to a current monitor 134 within the PVWG 150 or attached to the PVWG 150. Accordingly, the input channel 110 ₂ receives the input pulsed voltage waveform 140 ₂ and the conditioning circuit 111 ₂ generates output waveform (conditioned waveform) 144 ₂. In one example, as shown in FIG. 1B, a received or measured input pulsed voltage waveform 140 ₂ includes voltage pulses that include positive and negative voltage levels within different phases of each of the voltage pulses and high frequency oscillations within at least one of the phases of each pulse within the input pulsed voltage waveform 140 ₂ (e.g., see the dashed circle highlighting a region of a pulse), which when conditioned by the components, such as a voltage divider and a low pass filter, within the conditioning circuit 111 ₂ forms an output waveform 144 ₂ that is a filtered waveform that is at a reduced voltage level.

Further, the input channel 110 ₃ is connected to the current sense resistor 139 of the PVWG 150. Accordingly, the input channel 110 ₃ receives the input pulsed voltage waveform 140 ₃ and the conditioning circuit 111 ₃ generates output waveform (conditioned waveform) 144 ₃. In one example, as shown in FIG. 1B, a received or measured input pulsed voltage waveform 140 ₃ includes positive voltage pulses and high frequency oscillations within at least one of the phases of each pulse within the input pulsed voltage waveform 140 ₃ (e.g., see the dashed circle), which when conditioned by the components within the conditioning circuit 111 ₃, such as a low pass filter, forms an output waveform 144 ₃ that is a filtered waveform.

In some embodiments, additional input channels, such as input channels 110 ₄-110 _(N), are connected to other connection points within the plasma processing system 50 to receive additional information about the delivered pulsed voltage waveforms and/or state of a plasma process being performed in a plasma processing chamber. Further, the conditioning circuit 111 _(N) is configured to generate a corresponding output waveform 144 _(N). Input channel 110 _(N) receives the input pulsed voltage waveform 140 _(N) and the conditioning circuit 111 _(N) generates output waveform (conditioned waveform) 144 _(N). Thus, any of the conditioning circuits 111, such as conditioning circuit 111 _(N), may include any combination of voltage dividers 112 (FIG. 2) and low pass filters 114 (FIG. 3), or neither a voltage divider 112 nor a low pass filter 114.

As is illustrated in FIG. 1B, each of the input pulsed voltage waveforms 140 _(1A)-140 ₃ differ from each other. Accordingly, the corresponding output waveforms 144 _(1A)-144 ₃ differs from each other. Therefore, depending on the location that an input end of an input channel 110 is connected to the plasma processing system 50, the characteristics of the input pulsed voltage waveforms and output waveforms will vary accordingly, and thus the selection of a connection position of each of the input channels will have an effect on the information received by the feedback loop 100's which can affect the ability of the feedback loop 100 to control the pulsed voltage waveform.

Fast Data Acquisition Module

The fast data acquisition module 120 is generally configured to receive analog voltage waveforms (e.g., conditioned waveforms 144) and transmit digitized voltage waveforms. The fast data acquisition module 120 includes one or more acquisition channels 122 that are each electrically coupled to a respective conditioning circuit 111 of a first input channel 110, and the fast data acquisition module 120 is configured to generate a digitized voltage waveform from a received conditioned voltage waveform (e.g., the output waveform 144), wherein a data acquisition controller 123 of the fast data acquisition module 120 is configured to determine one or more waveform characteristics of the conditioned voltage waveform (e.g., the output waveform 144) by analyzing the first digitized voltage waveform. As illustrated in FIG. 1B, the fast data acquisition module 120 comprises a plurality of acquisition channels 122 ₁-122 _(N), a data acquisition controller 123 and memory 124 (e.g., non-volatile memory). Each of the acquisition channels 122 is electrically coupled to the output of a corresponding one of the input channels 110 such that an acquisition channel 122 receives an output waveform 144 from the corresponding one of the input channels 110. For example, the acquisition channel 122 ₁ is electrically coupled to the output end of the input channel 110 ₁ and receives either the output waveform 144 _(1A) or 144 _(1B), depending on the position of the connection point of input end of the input channel 110 ₁. Further, the acquisition channel 122 ₂ is electrically coupled to the output end of the input channel 110 ₂ and receives the output waveform 144 ₂. Additionally, or alternatively, the acquisition channel 122 ₃ is electrically coupled to the output end of the input channel 110 ₃ and receives the output waveform 144 ₃. The acquisition channel 122 _(N) is electrically coupled to the output end of the input channel 110 _(N) and receives the output waveform 144 _(N).

In some embodiments, the fast data acquisition module 120 is coupled to a feedback processor 125 via a data communication interface 125 _(A), wherein the feedback processor 125 is configured to generate one or more control parameters using one or more waveform characteristics determined by one or more algorithms that are executed by a processor within the data acquisition controller 123. The one or more algorithms, which are stored in memory 124, include instructions, which when executed by the processor 121 in the fast data acquisition module cause the fast data acquisition module to process the output waveform 144 (e.g., conditioned voltage waveform(s)) to determine one or more waveform characteristics of the received output waveform 144. As is discussed further below, the feedback processor 125 includes memory that includes instructions, which when executed by a processor (CPU) in the feedback processor 125 cause the feedback processor 125 to generate one or more control parameters using the determined one or more waveform characteristics provided from the fast data acquisition module 120. The instructions executed by the feedback processor may also be further configured to cause the feedback processor to transmit information related to the generated one or more control parameters to the PVWG 150. The PVWG 150 may also include memory that includes instructions, which when executed by a processor in the PVWG 150 causes the PVWG 150 to establish an adjusted pulsed voltage waveform based on the one or more control parameters generated by the feedback processor 125.

As discussed above, each of the acquisition channels 122 processes a corresponding output waveform 144 output by a corresponding input channel 110 to generate a digitized voltage waveform from the output waveform. For example, the acquisition channel 122 ₁ processes the output waveform 144 _(1A) or 144 _(1B) to generate a digitized voltage waveform. Further, the acquisition channel 122 ₂ processes the output waveform 144 ₂ to generate a digitized voltage waveform and the acquisition channel 122 ₃ processes the output waveform 144 ₃ to generate a digitized voltage waveform. Additionally, or alternatively, the acquisition channel 122 _(N) processes the output waveform 144 _(N) to generate a digitized voltage waveform.

The data acquisition module 120 further includes data acquisition controller 123. The data acquisition controller 123 is electrically coupled to output of each of the acquisition channels 122 and is configured to receive the digitized voltage waveform from each of the acquisition channels 122. Further, the algorithms stored within the memory 124 of the data acquisition controller 123 are adapted to determine one or more waveform characteristics of each of the conditioned waveforms (e.g., the output waveforms 144) by analyzing each of the digitized voltage waveforms. The analysis may include a comparison of information received in the digitized voltage waveform with information relating to one or more stored waveform characteristics that is stored in memory 124 and is discussed further below.

The data acquisition controller 123 can include one or more of an analog-to-digital converter (ADC) (not shown), a processor 121 (FIG. 1C), communication interface (not shown), a clock (not shown) and an optional driver (not shown). The processor may be any general computing processor. Further, the processor may be a Field Programmable Gate Array (FPGA). The ADC converts the signal within the output waveforms 144 from the analog domain to the digital domain and the output digital signal of the ADC is provided to the processor 121 for processing. The processor 121 of the data acquisition controller 123 determines the one or more waveform characteristics of the output waveform by analyzing the output digital signal provided from the ADC.

In various embodiments, the data acquisition module 120 additionally includes memory 124. The memory 124 may be any non-volatile memory. Further, the data acquisition controller 123 is electrically coupled with the memory 124 and is configured to cause waveform characteristics to be stored within the memory 124. In various embodiments, the memory 124 includes instructions executable by the data acquisition controller 123 to cause the data acquisition controller 123 to analyze the received output waveforms 144 and/or transmit information corresponding to determined waveform characteristics based on the analysis of the received output waveforms 144.

In various embodiments, the memory 124 includes one or more of a data logger 124A, a waveform analyzer 124B, and executable instructions 124C. The data acquisition controller 123 may be configured to store information corresponding to the waveform characteristics within the data logger 124A of the memory 124. For example, the data logger 124A may be include a database accessible by the data acquisition controller 123 to store information corresponding to the waveform characteristics. The waveform analyzer 124B includes instructions executable by the data acquisition controller 123 and when executed cause the data acquisition controller 123 to analyze the output waveforms 144 to determine the waveform characteristics. The executable instructions 124C are executable by the data acquisition controller 123 and when executed cause the data acquisition controller 123 to transmit waveform characteristics or information corresponding to the waveform characteristics to one or more of the feedback processor 125, the controller 127, the controller 128, and the controller 191. In one embodiment, the executable instruction 124C, when executed by the data acquisition controller 123, cause the data acquisition controller 123 to store the waveform characteristics within the data logger 124A, and analyze the waveform characteristics with regard to one or more threshold values, among others.

The data acquisition controller 123 is configured to receive and/or analyze the digitized voltage waveforms from each of the corresponding acquisition channels 122 in parallel. Alternatively, the data acquisition controller 123 is configured to receive and/or analyze the digitized voltage waveforms from each of the corresponding acquisition channels 122 serially.

As discussed above, the data acquisition module 120 may be electrically (wired or wirelessly) coupled with a feedback processor 125. The feedback processor 125 may be any general computing processor. In some embodiments, the feedback processor 125 is generally one of: an external processor connected to the fast data acquisition module 120 via a data communication interface; an internal processor integrated within the fast data acquisition module 120; or a controller for a substrate processing chamber (e.g., processing chamber controller 126) connected to the fast data acquisition module via a data communication interface. The data acquisition module 120 may communicate information corresponding to one or more of the received output waveforms 144 to the feedback processor 125. For example, the data acquisition module 120 may communicate information related to one or more detected and/or processed waveform characteristics of the one or more of the received output waveforms 144 to the feedback processor 125. Further, the feedback processor 125 may be communicatively coupled with the plasma processing system 50. In various embodiments, as discussed above, the feedback processor 125 includes a memory or is coupled to a memory, and the memory further contains a software algorithm for instructing a processor within the feedback processor 125 to perform one or more portions of the methods described herein.

In one or more embodiments, the data acquisition module 120 may be electrically (wired or wirelessly) coupled with a processing chamber controller 126 of a processing chamber (e.g., the processing chamber 800 of FIG. 8A) or a processing system that includes a processing chamber. For example, the data acquisition module 120 transmits data to and/or receives data from the processing chamber controller 126 (FIG. 1D). For example, the data acquisition module 120 communicate information related to one or more waveform characteristics to the processing chamber controller 126. Further, the processing chamber controller 126 may be communicatively coupled with the plasma processing system 50. In various embodiments, the processing chamber controller 126 is omitted. The processing chamber controller 126 may separately contain a controller CPU (not shown), non-volatile memory (not shown), graphical user interface (GUI) (not shown) and other useful hardware and software components which can be coded and stored within the memory for instructing the CPU. An algorithm stored within the memory of the processing chamber controller 126 can include instructions, which when executed by the controller CPU cause various process chamber set points to be adjusted, such as a chucking voltage set point on a chucking power supply, based on the information related to one or more waveform characteristics determined by the data acquisition controller 123.

In one or more embodiments, the data acquisition module 120 is electrically (wired or wirelessly) coupled with a controller 127 that includes a removable memory device. For example, the data acquisition module 120 transmits data to and/or receives data from the controller 127. For example, the data acquisition module 120 communicates information related to one or more waveform characteristics to the removable memory device of the controller 127.

In various embodiments, the data acquisition module 120 is electrically (wired or wirelessly) coupled to an external computing device via a communication interface. The data acquisition module 120 transmits data to and/or receives data from an external computing device (e.g., a computing device external to the fast data acquisition module 120). For example, the data acquisition module 120 communicates (e.g., transmits and/or receives data) with a controller of a computing device, such as the controller 128 (FIG. 1B-1D). The data acquisition module 120 may communicate one or more detected and/or processed waveform characteristics to the controller 128. The controller 128 may be a personal computer (PC), or a mobile computing device, among others. Further, the controller 128 may be communicatively coupled (e.g., via an Ethernet connection) with the data acquisition module 120 and/or the plasma processing system 50. In various embodiment, the controller 128 is omitted.

As will be described in greater detail in the description below and description of FIGS. 5A-5D, determining one or more waveform characteristics will generally include, but is not limited to determining one or more of a period of one-cycle of a pulse (T_(cycle)), a rise time of a pulse (T_(rise)), a fall time of a pulse (T_(fall)), offset of a pulse from a reference voltage (e.g., zero volts), an amplitude of pulse, a pulse width, a direct current (DC) voltage offset and a pulse waveform characteristic created during one or more of the phases of a pulse voltage waveform, such as the ion current phase (also referred to herein as the “ion current” waveform characteristic). Additionally, or alternatively, determining one or more waveform characteristics comprises determining waveform characteristics of a burst of pulses (e.g., T_(on) period, T_(off) period), as illustrated in FIG. 7B.

FIG. 1C illustrates a portion of a feedback loop 100A, according to one or more embodiments. The feedback loop 100A is configured similar to that of the feedback loop 100 of FIG. 1B. For example, the feedback loop 100A includes fast data acquisition module 120 including the acquisition channels 122, the data acquisition controller 123A, and the memory 124. However, as compared to the feedback loop 100 of FIG. 1B, the feedback processor 125 may be integrated within a processing chamber controller 126. The integrated feedback processor 125, in this case, may include a processor 126B and a memory 126A, which includes a data logger and an algorithm solver (e.g., software instructions for determining control parameters). In the configuration illustrated in FIG. 1C, the feedback loop 100 may not include an individual feedback processor 125, since the functions of the feedback processor 125 are carried out by the components within a processing chamber controller 126.

FIG. 1D illustrates a portion of a feedback loop 100B, according to one or more embodiments. The feedback loop 100B is configured similar to that of the feedback loop 100 of FIG. 1B. For example, the feedback loop 100B includes fast data acquisition module 120 including the acquisition channels 122, and the memory 124′. However, as compared to the feedback loop 100 of FIG. 1B, the feedback loop 100B does not include the feedback processor 125. For example, in the embodiment of FIG. 1D, the data acquisition controller 123B comprises the functionality of the data acquisition controller 123 of FIG. 1B and the feedback processor 125 of FIG. 1B. In such an embodiment, the data acquisition controller 123B functions to both analyze the output waveforms 144 to determine the waveform characteristics and to determine and communicate control parameters to the PVWG 150.

In one or more embodiments, a data acquisition controller 123 is coupled to a monitor 129 within a controller 191 via a digital interface. For example, the data acquisition controller 123 is coupled to the controller 191 and monitor 129 via a digital visual interface (DVI), a high-definition multimedia interface (HDMI), or a video graphics array (VGA), among others. The data acquisition controller 123 communicates information corresponding to one or waveform characteristics to the monitor 129 to be displayed on the monitor 129 for viewing by a user.

FIG. 2 is a schematic illustration of a voltage divider (e.g., the voltage divider 112) of a conditioning circuit 111, according to one or more embodiments. As illustrated in FIG. 2, the voltage divider 112 may include a first cascade voltage divider 210 and a second voltage divider cascade 212. The voltage divider 112 is electrically coupled to a low pass filter 114 via one or more electrical connections, such as signal line 221 and ground reference line 223. The first cascade voltage divider 210 includes resistor R1, resistor R2, capacitor C1, and capacitor C2. The second cascade voltage divider 212 includes resistor R4, resistor R5, capacitor C3, and capacitor C4. The resistance of resistor R1, the resistance of resistor R2, the capacitance of capacitor C1, and the capacitance of capacitor C2 are selected to generate a first voltage divider ratio. For example, the first voltage divider ratio may be in a range of about 20 to 1 to about 60 to 1. Further, the resistance of resistor R1 is greater than the resistance of resistor R2 and the capacitance of capacitor C2 is greater than the capacitance of capacitor C1. For example, the resistance of resistor R1 may be about 950 kilo-ohms and the resistance of resistor R2 may be about 20 kilo-ohms. Alternatively, the resistance of resistor R1 may be less than or greater than 950 kilo-ohms and the resistance of resistor R2 may be less than or greater than 20 kilo-ohms. Additionally, the capacitance of capacitor C2 may be about 650 pF and the capacitance of capacitor C1 may be about 15 pF. Alternatively, the capacitance of capacitor C2 may be less than or greater than 650 pF and the capacitance of capacitor C1 may be less than or greater than 15 pF.

The resistance of resistor R4, the resistance of resistor R5, the capacitance of capacitor C3, and the capacitance of capacitor C4 are selected to generate a second voltage divider ratio of the second voltage divider cascade 212. In some embodiments, the second voltage divider ratio is greater than the first voltage divider ratio. For example, the second voltage divider ratio may be in a range of about 80 to 1 to about 120 to 1. Further, the resistance of resistor R4 is greater than the resistance of resistor R5 and the capacitance of capacitor C4 is greater than the capacitance of capacitor C1. For example, the resistance of resistor R4 may be about 1000 kilo-ohms and the resistance of resistor R5 may be about 10 kilo-ohms. Alternatively, the resistance of resistor R4 may be less than or greater than 1000 kilo-ohms and the resistance of resistor R5 may be less than or greater than 10 kilo-ohms. Additionally, the capacitance of capacitor C4 may be about 1.5 nF and the capacitance of capacitor C3 may be about 15 pF. Alternatively, the capacitance of capacitor C4 may be less than or greater than 1.5 nF and the capacitance of capacitor C3 may be less than or greater than 15 pF.

In some embodiments, the first cascade voltage divider 210 is coupled to the second cascade voltage divider cascade 212 via resistor R3. The resistance of resistor R3 can be, for example, about 200 kilo-ohms. Alternatively, the resistance of resistor R3 may be greater than or less than about 200 kilo-ohms. The resistor R3 may filter out high frequencies from the input pulsed voltage waveform 140. The voltage divider ratio of the voltage divider 112 may be varied by altering the value of the capacitors C1-C4 and the resistors R1, R2, R4, and R5. For example, increasing the difference between R1 and R2 and C1 and C2 and/or increasing the difference between R4 and R5 and C3 and C4 increases the voltage divider ratio and decreasing the difference between R1 and R2 and C1 and C2 and/or decreasing the difference between R4 and R5 and C3 and C4 decreases the voltage divider ratio. In some embodiments, the first voltage divider cascade 210 has a dividing ratio in a range of about 10 to 1 to about 100 to 1, and the second voltage divider cascade 212 has a dividing ratio in a range of about 20 to 1 to about 120 to 1.

In embodiments where the input channel 110 includes the voltage divider 112 and the low pass filter 114, the input of the low pass filter 114 is electrically coupled to the output of the voltage divider 112 such that the low pass filter 114 receives the divided voltage waveform from the voltage divider 112. Further, the low pass filter 114 has a frequency response curve comprising a plateau and a cut-off frequency. For example, the filter response of the low pass filter 114 has a plateau at frequencies less than a bandwidth frequency of about −3 dB. The plateau of the low pass filter 114 is in a range of DC to about 7 MHz and the cut-off frequency is in a range of about 5 MHz to about 10 MHz. FIG. 4 illustrates an example of a frequency response curve (e.g., frequency response curve 400) of a low pass filter 114. As illustrated, the filter response curve has a plateau at frequencies less than the bandwidth (e.g., −3 dB) frequency of about 7.3 MHz. Alternatively, the bandwidth frequency may be greater than or less than about 7.3 MHz.

FIG. 3 is a schematic illustration of a low pass filter (e.g., the low pass filter 114) of the conditioning circuit 111, according to one or more embodiments. As illustrated in FIG. 3, the low pass filter 114 includes a filter cascade 222 and a filter cascade 224. The filter cascade 222 may be a 2-stage Chebyshev filter. For example, the filter cascade 222 may be a 2-stage Chebyshev filter having a stop band attenuation of about 0.1 dB. Alternatively, 2-stage Chebyshev filters having a stop band attenuation of less than or greater than 0.1 dB may be utilized. The filter cascade 222 comprises resistors R6, R7, capacitors C6 and C5 and operational amplifier 225. The resistance of the resistors R6 and R7 may be the same. For example, the resistance of resistors R6 and R7 may be about 50 ohms. However, other resistance values may be utilized. Further, in one example, the capacitance of capacitor C6 may be about 360 pF and the capacitance of capacitor C5 may be about 147 pF. However, other capacitance values may be utilized. Additionally, the filter cascade 222 may have a cut-off frequency of about 15 MHz. Alternatively, the filter cascade 222 may have a cut-off frequency of less than or greater than about 15 MHz.

An input of the filter cascade 224 is electrically coupled to the output of the filter cascade 222. The filter cascade 224 is an LCL filter cascade. Further, the filter cascade 224 may be a 5th order Butterworth filter. Additionally, the filter cascade 224 may have a cut-off frequency less than the cut-off frequency of the filter cascade 222. For example, the filter cascade 224 may have a cut-off frequency of about 7.3 MHz. Alternatively, the filter cascade 224 may have a cut-off frequency of less than or greater than about 7.3 MHz. The filter cascade 224 includes resistors R8, R9, inductors L1, L3, and L3, and capacitors C10 and C11. The resistance of resistor R8 may be about 400 kilo-ohms; however, other resistance values may be utilized. Further, the inductance of inductor L1 may be about 5.4 uH, the inductance of inductor L2 may be about 17.5 uH, and the inductance of inductor L3 may be about 5.4 uH. However, other inductance values may be utilized. Additionally, the inductance of the inductor L2 is greater than that of inductor L1 and L2. Further, the inductance of inductor L1 may be equal to the inductance of inductor L3. The capacitance of the capacitors C10 and C11 may be the same. For example, the capacitance of the capacitors C10 and C11 may be about 88 pF. However, other capacitance values may be utilized. Further, the resistance of resistors R8 and R9 may be about 400 kilo-ohms. However, other resistance values may be used.

In some embodiments, the filter cascade 222 and filter cascade 224 each have a frequency response curve comprising a plateau and a cut-off frequency, wherein the plateau is between 1 MHz and about 7 MHz, and the cut-off frequency is in a range of about 5 MHz to about 10 MHz.

FIGS. 5A, 5B, 5C, and 5D illustrate output waveforms (i.e., conditioned waveforms) 144 _(1A), 144 _(1B), 144 ₂, and 144 ₃, respectively. The output waveforms illustrated in FIGS. 5A, 5B, 5C, and 5D include a periodic series of short pulses repeating with a period “T_(cycle)” (e.g., 2.5 microseconds), on top of a voltage offset. In one plasma processing example, as is discussed below, the short pulse forms only about 10% of the period “T_(cycle)”.

As briefly discussed above, and shown FIG. 5A, the output waveform 144 _(1A) may be analyzed by the acquisition channel 122 ₁ to determine the waveform characteristics including one or more of a period of one-cycle of a pulse (T_(cycle)), a rise time of a pulse (T_(rise)), a fall time of a pulse (T_(fall)), and DC voltage offset of a pulse from a reference voltage (e.g., zero volts). In one embodiment, the conditioning circuit 111 _(1A) of the input channel 110 ₁, which is coupled to the biasing electrode 804 (FIG. 8A) side of the generator coupling assembly 133, only includes a voltage divider 112, which is used to form the output waveform 144 _(1A). In this configuration, due to the absence of the low pass filter 114, a correct determination of the pulse timing characteristics (e.g., period, rise time, fall time, etc.) can be achieved. Also, in some embodiments, a chucking force applied to a substrate, by use biasing electrode 804 (FIG. 8A) and high DC voltage power supply V_(hvm) of a HVM 816 (FIG. 8B), can also be determined by measuring the difference between the DC voltage on biasing electrode 804 (FIG. 8A) and the substrate 803.

Further, as illustrated in FIG. 5B, the output waveform 144 _(1B) may be analyzed by the acquisition channel 122 ₁ to determine the waveform characteristics including amplitude “Ampl” of a pulse, pulse width “W”, and DC voltage offset. The determined pulse width “W” can equal the full width at half maximum. In one embodiment, the conditioning circuit 111 _(1B) of the input channel 110 ₁, which has an input end of the input channel 110 ₁ coupled to the generator side of the generator coupling assembly 133, includes a voltage divider 112 and a low pass filter 114, which are used to form the output waveform 144 _(1B). In this configuration, a determination of the sheath voltage (V_(sh)) (FIG. 10B) and ion energy (E_(i)) can be achieved during plasma processing by the prior determination of a scaling factor (α), wherein the E_(i)≈V_(sh)≈α·“Ampl”. Also, in some embodiments, a chucking force applied to a substrate can be determined by measuring the difference between the DC voltage on the biasing electrode 804 (FIG. 8A) and the substrate 803. Also, characteristics of an ion current (I_(ion)) generated within an ion current phase of a pulse waveform can be determined, which is discussed further below.

As illustrated in FIG. 5C, the output waveform 144 ₂ may be analyzed by the acquisition channel 122 ₂ to determine the waveform characteristics including an ion current offset. In one embodiment, the conditioning circuit 111 ₂ of the input channel 110 ₂, which has an input end of the input channel 110 ₂ coupled to a current monitor 134 (FIGS. 1B and 9B), includes a voltage divider 112 and a low pass filter 114, which are used to form the output waveform 144 ₂. In this configuration, a determination of information relating to the ion current offset can be achieved during plasma processing by use of the equation I_(ion)=(Ion Current Offset)/factor, where “I_(ion)” is the ion current and “factor” is the volts-per-amp output characteristic of the current monitor 134.

Additionally, or alternatively, the output waveform 144 ₃ (FIG. 5D) may be analyzed by the acquisition channel 122 ₃ to determine the waveform characteristics including a maximum ion current during plasma processing. In one embodiment, the conditioning circuit 111 ₃ of the input channel 110 ₃, which has an input end of the input channel 110 ₃ coupled to a current sense resistor 139 within a PVWG 150, only includes a low pass filter 114, which is used to form the output waveform 144 ₃. In this configuration, due to the absence of the voltage divider 112, a correct determination of the magnitude of ion current (I_(ion)) can be achieved. A determination of the maximum ion current “Max” can be achieved during plasma processing by use of the equation I_(ion)=(Max)/R_(sense), where “R_(sense)” is the value of the R_(sense) resistor.

The feedback processor 125 may receive information regarding one or more of waveform characteristics from the fast data acquisition module 120 and generates corresponding control parameters. The feedback processor 125 communicates the control parameters to the PVWG 150 and the PVWG 150 adjusts the pulsed voltage waveform established on the complex load 130 based on the received control parameters. For example, the PVWG 150 may increase an amplitude and/or width of the pulse voltage waveform established on the complex load 130 based on the received control parameters. Adjusting the parameters utilized to generate the pulsed voltage waveform can be used to mitigate undesirable changes or process variable drift within the processing chamber during substrate processing. For example, adjusting the parameters utilized to generate the pulsed voltage waveform may mitigate changes to the sheath voltage and the ion energy distribution function at the substrate during plasma processing, which are discussed in more detail below. Changes to the sheath voltage (V_(sh)) and the ion energy distribution function may occur in response to changes in the load, drifts in the plasma density, changes to the condition of the chamber walls, substrate temperature, and/or degree and state of chemical dissociation.

With further reference to FIG. 1B, the PVWG 150 establishes a pulsed voltage waveform on the complex load 130 via the generator coupling assembly 133. The PVWG 150 may establish the pulsed voltage waveform based on control parameters derived from the waveform characteristics (e.g., amplitude, pulse width, DC offset and ion current) determined by the data acquisition module 120. In the simplest case, the waveform characteristics determined by the data acquisition module 120 may be provided to a user (e.g., displayed on a monitor of the controller 127), which then adjusts the control parameters used by the PVWG 150 to improve the pulsed waveform characteristics of one or more pulse waveforms generated by the PVWG 150 based on the determined waveform characteristics. The control parameters may alternately be received from the feedback processor 125, the controller 128, or the processing chamber controller 126. The control parameters may include information that are used by the PVWG 150 to form a subsequently generated adjusted pulse voltage waveform, and the control parameters may include, but are not limited to one or more of: the determined one or more waveform characteristics of the first conditioned voltage waveform have reached their target values or limits; a maximum limit of a DC charge voltage is reached; a maximum power limit is reached; a maximum time limit for algorithm convergence is reached; a maximum limit of a pulse width is reached; and a minimum limit of a pulse width is reached. The control parameters may be communicated to the PVWG 150 at a predetermined rate. The predetermined rate may be about 10 transmissions per second. Alternatively, the predetermined rate may be less than or greater than 10 transmissions per second.

Additionally, or alternatively, the processing chamber controller 126 may receive one or more waveform characteristics from the fast data acquisition module 120 and then generate corresponding control parameters. The processing chamber controller 126 may communicate the control parameters to the PVWG 150. Alternatively, the processing chamber controller 126 may communicate the control parameters to the feedback processor 125, and the feedback processor 125 communicates the control parameters to the PVWG 150. The PVWG 150 adjusts the input pulsed voltage waveform 140 output by the PVWG 150 based on the determined control parameters. The PVWG 150 may increase an amplitude and/or width of the pulse voltage waveform output by the PVWG 150. Further, the processing chamber controller 126 may be configured to provide target amplitude and pulse width, as well as values for control parameters at least once per process recipe. Additionally, the fast data acquisition module 120 may communicate one or more of the amplitude, the pulse width, and the DC offset of the output waveform 144 at a transmission rate. For example, the transmission rate may be about 10 transmissions per second. However, transmission rates of greater than or less than 10 transmissions per second may be utilized.

Additionally, or alternatively, the controller 128 may receive one or more of the amplitude, the pulse width, the DC offset and an ion current from the fast data acquisition module 120 and then generate corresponding control parameters. Alternatively, the fast data acquisition module 120 may communicate a processed waveform to the controller 128, and the controller 128 may determine one or more control parameters from the waveform. The controller 128 communicates the control parameters to the PVWG 150, and the PVWG 150 adjusts the pulsed voltage waveform output by the PVWG 150 based on the determined control parameters. Alternatively, the controller 128 communicates the control parameters to the feedback processor 125, which transmits the control parameters to the PVWG 150, and the PVWG 150 adjusts the pulsed voltage waveform output by the PVWG 150 based on the determined control parameters.

FIGS. 6A and 6B include examples of a portion of one waveform cycle of input and conditioned (e.g., divided and filtered) voltage waveforms originating from the signal source 1B (generator end of the generator coupling assembly), measured using an embodiment of a data acquisition system comprising a conditioning circuit and a fast data acquisition module. Digital information contained in a portion of a waveform recorded over this length of time can be analyzed by a data acquisition controller 123 to determine voltage waveform characteristics, such as amplitude (Ampl), full width at half maximum (W), and offset. Specifically, FIG. 6A illustrates a portion of one waveform cycle of the input pulsed voltage waveform 140 _(1B) and a divided waveform 610. The divided waveform may generated by voltage dividing the input pulsed voltage waveform 140 _(1B). For example, with reference to FIG. 1B, the voltage divider of the conditioning circuit 111 _(1B) voltage divides the input pulsed voltage waveform 140 _(1B). FIG. 6B illustrates a portion of one waveform cycle of the input pulsed voltage waveform 140 _(1B) and the output waveform 144 _(1B). The output waveform 144 _(1B) may be generated by low pass filtering the divided waveform 610 (FIG. 6A). In various embodiments, the output waveform 144 _(1B) may be analyzed by the data acquisition controller 123 to determine one or more waveform characteristics.

FIG. 7A illustrates multiple cycles of the input pulsed voltage waveform 140 _(1B). More specifically, FIG. 7A includes an example of multiple cycles (pulses) of an input voltage waveform originating from the signal source 1B (generator end of the generator coupling assembly), measured using an embodiment of a data acquisition system comprising a conditioning circuit and a fast data acquisition module. As is described with regard to FIG. 1B, the input pulsed voltage waveform 140 _(1B) may be received by the input channel 110 _(1B) and analyzed by the acquisition channel 1201 to determine one or more waveform characteristics. Digital information contained in a waveform recorded over this length of time can be analyzed by a data acquisition controller 123 to determine such voltage waveform characteristics as amplitude (Ampl), offset (offset), a pulse period (T_(P)), and a pulse repetition frequency (f_(P)=1/T_(P)).

FIG. 7B illustrates multiple bursts 710 of the input pulsed voltage waveform 140 _(1B). Each of the bursts 710 has a burst period including an on time 720 and an off time 732. Further, the frequency of the input pulsed voltage waveform 140 _(1B) is based on the burst period and the burst duty cycle is based on the on time 720 and the burst period. More specifically, FIG. 7B includes an example of multiple bursts (each containing a plurality of waveform cycles) of an input pulsed voltage waveform originating from the signal source 1B (generator end of the generator coupling assembly), measured using an embodiment of a data acquisition system comprising a conditioning circuit and a fast data acquisition module. Digital information contained in a waveform recorded over this length of time can be analyzed by a data acquisition controller to determine such voltage waveform characteristics as offset (offset), a burst period (T_(B)=T_(on)+T_(off)), a burst frequency (f_(B)=1/T_(B)), and a burst duty cycle (Duty=T_(on)/T_(B)).

Plasma Processing Chamber Example

FIG. 8A is a schematic cross-sectional view of a processing chamber 800, in which the complex load 130 is formed during plasma processing. The processing chamber 800 is configured to practice the biasing schemes proposed herein, according to one embodiment. In one embodiment, the processing chamber is a plasma processing chamber, such as a reactive ion etch (RIE) plasma chamber. In some other embodiments, the processing chamber is a plasma-enhanced deposition chamber, for example a plasma-enhanced chemical vapor deposition (PECVD) chamber, a plasma enhanced physical vapor deposition (PEPVD) chamber, or a plasma-enhanced atomic layer deposition (PEALD) chamber. In some other embodiments, the processing chamber is a plasma treatment chamber, or a plasma based ion implant chamber, for example a plasma doping (PLAD) chamber. Herein, the processing chamber includes an inductively coupled plasma (ICP) source electrically coupled to a radio frequency (RF) power supply. In other embodiments, the plasma source is a capacitively coupled plasma (CCP) source, such as a source electrode disposed in the processing volume facing the substrate support, wherein the source electrode is electrically coupled to an RF power supply.

The processing chamber 800 features a chamber body 813 which includes a chamber lid 823, one or more sidewalls 822, and a chamber base 824 which define a processing volume 826. A gas inlet 828 disposed through the chamber lid 823 is used to provide one or more processing gases to the processing volume 826 from a processing gas source 819 in fluid communication therewith. Herein, a plasma generator is configured to ignite and maintain a processing plasma 801 from the processing gases includes one or more inductive coils 817 disposed proximate to the chamber lid 823 outside of the processing volume 826. The one or more inductive coils 817 are electrically coupled to an RF power supply 818 via an RF matching circuit 830. The plasma generator is used to ignite and maintain a processing plasma 801 using the processing gases and electromagnetic field generated by the inductive coils 817 and RF power supply 818. The processing volume 826 is fluidly coupled to one or more dedicated vacuum pumps, through a vacuum outlet 820, which maintain the processing volume 826 at sub-atmospheric conditions and evacuate processing, and/or other gases, therefrom. A substrate support assembly 836, disposed in the processing volume 826, is disposed on a support shaft 838 sealingly extending through the chamber base 824.

The substrate 803 is loaded into, and removed from, the processing volume 826 through an opening (not shown) in one of the one or more sidewalls 822, which is sealed with a door or a valve (not shown) during plasma processing of the substrate 803. Herein, the substrate 803 is transferred to and from a receiving surface of an ESC substrate support 805 using a lift pin system (not shown).

The substrate support assembly 836 includes a support base 807 and the ESC substrate support 805 that is thermally coupled to, and disposed on, the support base 807. Typically, the support base 807 is used to regulate the temperature of the ESC substrate support 805, and the substrate 803 disposed on the ESC substrate support 805, during substrate processing. In some embodiments, the support base 807 includes one or more cooling channels (not shown) disposed therein that are fluidly coupled to, and in fluid communication with, a coolant source (not shown), such as a refrigerant source or water source having relatively high electrical resistance. In some embodiments, the ESC substrate support 805 includes a heater (not shown), such as a resistive heating element embedded in the dielectric material thereof. Herein, the support base 807 is formed of a corrosion resistant thermally conductive material, such as a corrosion resistant metal, for example aluminum, aluminum alloy, or stainless steel and is coupled to the substrate support with an adhesive or by mechanical means. Typically, the ESC substrate support 805 is formed of a dielectric material, such as a bulk sintered ceramic material, such as a corrosion resistant metal oxide or metal nitride material, for example aluminum oxide (Al₂O₃), aluminum nitride (AlN), titanium oxide (TiO), titanium nitride (TiN), yttrium oxide (Y₂O₃), mixtures thereof, or combinations thereof. In embodiments herein, the ESC substrate support 805 further includes a biasing electrode 804 embedded in the dielectric material thereof. In one configuration, the biasing electrode 804 is a chucking pole used to secure (chuck) the substrate 803 to a supporting surface of the ESC substrate support 805 and to bias the substrate 803 with respect to the processing plasma 801 using a pulsed-voltage biasing scheme described herein. Typically, the biasing electrode 804 is formed of one or more electrically conductive parts, such as one or more metal meshes, foils, plates, or combinations thereof. Herein, the biasing electrode 804 is electrically coupled to a HVM 816, which provides a chucking voltage thereto, such as static DC voltage between about −5000 V and about 5000 V, using an electrical conductor, such as the coaxial transmission line 806, e.g., a coaxial cable.

The support base 807 is electrically isolated from the chamber base 824 by an insulator plate 811, and a ground plate 812 is interposed between the insulator plate 811 and the chamber base 824. In some embodiments, the processing chamber 800 further includes a quartz pipe 810, or collar, circumscribing the substrate support assembly 836 to prevent corrosion of the ESC substrate support 805 and, or, the support base 807 from contact with corrosive processing gases or plasma, cleaning gases or plasma, or byproducts thereof. Typically, the quartz pipe 810, the insulator plate 811, and the ground plate are circumscribed by a liner 808. Herein, a plasma screen 809 approximately coplanar with the substrate receiving surface of the ESC substrate support 805 prevents plasma from forming in a volume between the liner 808 and the one or more sidewalls 822.

The biasing electrode 804 is spaced apart from the substrate receiving surface of the ESC substrate support 805, and thus from the substrate 803, by a layer of dielectric material of the ESC substrate support 805. In this configuration, a parallel plate like structure is formed by the biasing electrode 804 and the layer of the dielectric material which can have an effective capacitance of between about 5 nF and about 50 nF. Typically, the layer of dielectric material has a thickness between about 0.1 mm and about 1 mm, such as between about 0.1 mm and about 0.5 mm, for example about 0.3 mm. Herein, the biasing electrode 804 is electrically coupled to the PVWG 150 using the external conductor, such as the transmission line 806, which is disposed within the transmission line 131. The PVWG 150 and the components thereof are described in detail earlier in the text of this disclosure. In some embodiments, the dielectric material and layer thickness can be selected so that the capacitance C_(e) of the layer of dielectric material is between about 5 nF and about 50 nF, such as between about 7 and about 10 nF, for example.

Generally, a low neutral fill pressure in the processing volume 826 of the processing chamber 800 results in poor thermal conduction between surfaces disposed therein, such as between the dielectric material of the ESC substrate support 805 and the substrate 803 disposed on the substrate receiving surface thereof, which reduces the ESC substrate support's 805 effectiveness in heating or cooling the substrate 803. Therefore, in some processes, a thermally conductive inert heat transfer gas, typically helium, is introduced into a volume (not shown) disposed between a non-device side surface of the substrate 803 and the substrate receiving surface of the ESC substrate support 805 to improve the heat transfer therebetween. The heat transfer gas, provided by a heat transfer gas source (not shown), flows to the backside volume through a gas communication path (not shown) disposed through the support base 807 and further disposed through the ESC substrate support 805.

The processing chamber 800 further includes a processing chamber controller 126. The processing chamber controller 126 herein includes a central processing unit (CPU) 833, a memory 834, and support circuits 835. The processing chamber controller 126 is used to control the process sequence used to process the substrate 803 including the substrate biasing methods described herein. The CPU 833 is a general purpose computer processor configured for use in an industrial setting for controlling processing chamber and sub-processors related thereto. The memory 834 described herein may include random access memory, read only memory, floppy or hard disk drive, or other suitable forms of digital storage, local or remote. The support circuits 835 are conventionally coupled to the CPU 833 and comprise cache, clock circuits, input/output subsystems, power supplies, and the like, and combinations thereof. Software instructions (program) and data can be coded and stored within the memory 834 for instructing a processor within the CPU 833. A software program (or computer instructions) readable by CPU 833 in the processing chamber controller 126 determines which tasks are performable by the components in the processing chamber 800. Preferably, the program, which is readable by CPU 833 in the processing chamber controller 126, includes code, which when executed by the processor (CPU 833), perform tasks relating to the monitoring and execution of the electrode biasing scheme described herein. The program will include instructions that are used to control the various hardware and electrical components within the processing chamber 800 to perform the various process tasks and various process sequences used to implement the electrode biasing scheme described herein.

The PVWG 150 establishes a pulsed voltage waveform on a load (e.g., the complex load 130), which is formed by use of the biasing electrode 804. The PVWG 150 includes a nanosecond pulse generator 814 and a current-return output stage 815, which are schematically illustrated in FIGS. 8A and 8B. The nanosecond pulse generator 814 maintains a predetermined, substantially constant positive voltage across its output (i.e. to ground) during regularly recurring time intervals of a predetermined length, by repeatedly closing and opening its internal switch at a predetermined rate. FIG. 8A shows a simplified, functionally equivalent schematic representation of the nanosecond pulse generator 814. In FIG. 8A, the nanosecond pulse generator 814 is reduced to a minimal combination of the components that are important for understanding of its role in establishing a desired pulsed voltage waveform at the biasing electrode 804. These components generally include an internal voltage source, a high repetition rate switch, and a flyback diode, among others. It needs to be understood that an actual nanosecond pulse generator may include any number of internal components and may be based on a more complex electrical circuit than that of FIG. 8A. In turn, a schematic diagram of FIG. 8A provides only a functionally equivalent representation of the components of the nanosecond pulse generator 814 and its electrical circuitry, in as much as is required to explain the fundamental principle of its operation, its interaction with the plasma in the processing volume, and its role in establishing a pulsed voltage waveform (such as the input pulsed voltage waveform 140) at the biasing electrode 804. As can be inferred from a schematic diagram shown in FIG. 8A, when the switch S₁ moves from the open (Off) to the closed (On) position, it connects the output of the nanosecond pulse generator to its internal voltage source that produces a substantially constant output voltage. In one or more embodiments, the purpose of a flyback diode, which can also be substituted by a different snubber circuit, is to suppress, or “snub”, a possible voltage spike caused by opening of the switch S₁, which is followed by a rapid release of the magnetic energy accumulated in the inductive elements. These inductive elements comprise: (A) an external electrical conductor, such as the transmission line 806 with the combined inductance L_(transm), and (B) components of the PVWG 150, including an internal electrical conductor connecting the nanosecond pulse generator 814 and the current-return output stage 815, with the combined inductance L_(internal). The nanosecond pulse generator 814 may be primarily used as a charge injector (current source), and not as a constant voltage source; therefore it is not necessary to impose stringent requirements on the stability of the output voltage, in that it can vary in time even when the switch remains in the closed (On) position. Further, in some configurations, the nanosecond pulse generator 814 is fundamentally a sourcing, but not a sinking supply, in that it only passes a current in one direction (e.g., the output can charge, but not discharge a capacitor). Additionally, when the switch remains in the open (Off) position, the voltage V₀, across the output of the nanosecond pulse generator is not controlled by the internal voltage source and is instead determined by the interaction of its internal components with other circuit elements.

The current-return output stage 815 has one end 815B connected to ground, and another end 815A connected through the internal electrical conductor to the positive output of the nanosecond pulse generator and simultaneously to the external electrical conductor that is coupled to one side of the generator coupling assembly 133 (FIG. 1B). The current-return output stage 815 can be comprised of the following elements: a resistor, a resistor and an inductor connected in series, a switch, or a more complex combination of electrical elements, including parallel capacitors, which permits a positive current flow towards the ground.

Transmission line 131 electrically connects the output of the PVWG 150 to the chucking pole (e.g., biasing electrode 804). The output of the PVWG 150 is the end 815A, where the output of the nanosecond pulse generator 814 is connected through the internal electrical conductor to the current-return output stage 815. The electrical conductor of the transmission line 131, which is connected to the biasing electrode side of the generator coupling assembly 133 and to the biasing electrode 804, may include: (a) a coaxial transmission line 806, which may include a flexible coaxial cable with the inductance L_(flex) in series with a rigid coaxial transmission line with the inductance L_(rigid), (b) an insulated high-voltage corona-resistant hookup wire, (c) a bare wire, (d) a metal rod, (e) an electrical connector, or (f) any combination of electrical elements in (a)-(e). Note that the internal electrical conductor may comprise the same basic elements as the external electrical conductor.

The biasing electrode 804 is usually a metal plate embedded into the electrostatic chuck and separated from the plasma by a thin layer of dielectric material. The chucking pole can be the biasing electrode 804 embedded within the electrostatic chuck portion (i.e., ESC substrate support 805). The external conductor, such as the transmission line 806, and the biasing electrode 804 have some combined stray capacitance to ground, C_(s).

FIG. 8B depicts a functionally equivalent, simplified electrical circuit 840 of the pulsed voltage biasing scheme proposed herein, including the plasma in the process volume. These circuits are used to model the main aspects of the interaction of the pulsed voltage waveform generator (e.g., PVWG 150) with the processing chamber 800; explain the basic principle of operation and the role of the pulsed voltage waveform generator in establishing of the pulsed voltage waveform at a biasing electrode (e.g., biasing electrode 804); describe the accompanying physical phenomena taking place during different phases of the pulsed voltage waveform; and generally explain the basic principle of operation of a pulsed voltage biasing scheme. For clarity purposes, the following definitions are used throughout this disclosure: (1) unless a reference is specified, all potentials are referenced to ground; (2) the voltage at any physical point (like a substrate or a biasing electrode) is likewise defined as the potential of this point with respect to ground (zero potential point); (3) the cathode sheath is implied to be an electron-repelling, ion-accelerating sheath that corresponds to a negative substrate potential with respect to plasma; (4) the sheath voltage (also referred to sometimes as “sheath voltage drop”), V_(sh), is defined as the absolute value of the potential difference between the plasma and the adjacent surface (e.g. of the substrate or the chamber wall); and (5) the substrate potential is the potential at the substrate surface facing the plasma.

Firstly, the dielectric layer in the electrostatic chuck, and the processed substrate (e.g., a 0.3 to 0.8 mm thick doped-silicon slab with the capacitance of >10 nF) placed on its surface separate the chucking pole (e.g., biasing electrode 804) from the plasma and are represented in the circuits in FIG. 8B by a single chuck capacitor 843 (which in reality is two capacitors connected in series) with a capacitance C_(e) (˜7-10 nF, for example). In other words, the substrate (typically made out of a thin layer of a semiconductor and/or dielectric material) may be considered to be electrically a part of the ESC dielectric layer and whenever reference to the chuck capacitance C_(e) (i.e., item 843) is made, it is implied that C_(e) is the combined series capacitance of the ESC (i.e., C_(ESC) (˜dielectric layer capacitance)) and the substrate (i.e., C_(w)). Since the substrate capacitance C_(w) is typically very large (>10 nF), or substrate may be conductive (infinite capacitance), the series capacitance is determined primarily by the actual C_(ESC).

Secondly, the biasing electrode 804, the PVWG 150, and the external electrical conductor (e.g., transmission line 131) connecting biasing electrode 804 with the PVWG 150 have: (A) some combined stray capacitance to ground, which is represented by a single stray capacitor 842 with the capacitance C_(s) (˜500 pF, for example); as well as (B) some inductance, which is represented by inductors L_(internal) for the internal electrical conductor and other components of the PVWG 150, and inductances L_(interconnect) and L_(external) (i.e., items 845A and 845B) for the external electrical conductor, such as the transmission line 806. The current-return output stage 815 is represented in the circuit 840 by resistor R_(ros) (˜150 Ohm, for example) and inductor L_(ROS), which can also optionally include a switch S₂.

As shown in FIG. 8B, the PVWG 150 may also include a bypass resistor R_(bypass) and a current sensing circuit 821 that are connected in parallel with the current-return output stage 815. The current sensing circuit 821 includes the current sense resistor R_(sense) (i.e., item 139) and a switch S₃ that can be used to sense the current flowing through the current-return output stage 815 during one or more phases of a pulse.

Thirdly, a standard electrical plasma model that represents the entire plasma in the process volume as three series elements may be utilized. For example, an electron-repelling cathode sheath 844 (which we sometimes also refer to as the “plasma sheath” or just the “sheath”) adjacent to the substrate. The cathode sheath is represented in FIG. 8B by a conventional three-part circuit element comprising: (a) the diode D_(SH), which when open represents the sheath collapse, (b) the current source I_(L) (e.g., ˜0.5-5 A), representing the ion current flowing to the substrate in the presence of the sheath, and (c) the capacitor C_(SH) (˜100-300 pF, for example, for high aspect ratio applications), which represents the sheath for the main portion of the biasing cycle (˜90%), i.e., ion current phase (e.g., phase after the short pulse is delivered), during which the ion acceleration and the etching occur.

A bulk plasma 846 is represented in FIG. 8B by a single resistor of ˜5-10 Ohms. An electron-repelling wall sheath forming at the chamber wall is represented in FIG. 8B by a 3-part circuit element comprising: (a) the diode D_(w), (b) the current source I_(iw) (e.g., ˜5-10 A) representing the ion current to the wall, and (c) the capacitor C_(w) (e.g., ˜5-10 nF), which represents the wall sheath primarily during the ESC recharging phase, when there is no electron-repelling cathode sheath and the wall sheath capacitor is being charged by the large current pushed through the ESC by the nanosecond pulse generator. Because the cathode sheath is much thicker than the wall sheath (due to a high voltage), and the total wall area is much larger than the substrate area, it is assumed that C_(w)>>C_(SH). The interior surface of the grounded metal walls is considered be coated with a thin layer of a dielectric material, represented in FIG. 8B by a large capacitor C_(coat) (e.g., ˜300-1000 nF).

In some embodiments, as shown in FIGS. 8A and 8B, the system includes a high-voltage module (HVM) 816 used for chucking, such as “electrically clamping”, the substrate to the substrate receiving surface of the ESC substrate support, as shown in FIG. 8A. Chucking the substrate allows filling a gap between the substrate receiving surface and the non-device side surface of the substrate with helium gas (He), which is done in order to provide good thermal contact between the two and allow substrate temperature control by regulating the temperature of the ESC substrate support. Combining a DC chucking voltage produced by the HVM with the pulsed voltage produced by the PVWG 150 at a biasing electrode 804 will result in an additional voltage offset of the pulsed voltage waveform equal to the DC chucking voltage. The effect of the HVM 816 on the operation of the PVWG 150 can be made negligible by selecting appropriately large blocking capacitor C_(hvm) and R_(hvm2). The resistance R_(hvm2) schematically illustrates a resistor positioned within the components connecting the HVM 816 to a point within the transmission line 131. The main function of the blocking capacitor C_(hvm) of in the simplified electrical circuit 840 is to protect the PVWG 150 from the HVM DC voltage produced by the DC power supply V_(hvm), which thus drops across C_(hvm) and does not perturb the PVWG 150 output. The value of C_(hvm) is selected such that while blocking only the HVM DC voltage, it does not present any load to the pulsed bias generator's high-frequency output voltage. By selecting a sufficiently large C_(hvm) (e.g., 40-80 nF) the C_(hvm) is nearly transparent for a 400 kHz signal, for example, in that it is much bigger than any other relevant capacitance in the system and the voltage drop across this element is very small compared to that across other relevant capacitors, such as chuck capacitance C_(e), and sheath capacitance C_(SH). In turn, the purpose of the blocking resistor R_(hvm2) is to block the high-frequency pulsed bias generator's voltage and minimize the current it induces in the HVM DC voltage supply. This blocking resistor R_(hvm2) needs to be large enough to efficiently minimize the current through it. For example, an R_(hvm2)>1 MOhm is typically large enough to make the 400 kHz current from the pulsed bias generator into the HVM negligible. The resultant average induced current of the order of 0.5-1 mA is indeed much smaller than a typical limitation for HVM power supplies, which is about 5 mA DC current. The C_(hvm1) and R_(hvm1), and also the R_(hvm2), together form a current suppressing/filtering circuit for the pulsed voltage, so that pulsed voltage does not induce current through the HVM 816.

In some embodiments, the feedback loop 100 is coupled to one or more points within the PVWG 150 or along the electrical conductor disposed between the PVWG 150 and the blocking capacitor C_(hvm), which is disposed within the generator coupling assembly 133. For example, one or more input channels 110 of the feedback loop 100 is coupled via connection to one or more points along the electrical conductor disposed between the PVWG 150 and the blocking capacitor C_(hvm). Further, in some embodiments, one or more of the input channels 110 are electrically coupled via connection to one or more points along the electrical conductor disposed between the blocking capacitor C_(hvm) and the biasing electrode 804 in the processing chamber 800. For example, one or more input channels 110 are electrically coupled to one or more points along the electrical conductor disposed between the blocking capacitor C_(hvm) and the biasing electrode 804 in the processing chamber 800. Alternatively, in other embodiments, one or more of the input channels 110 are coupled to one or more points along the electrical conductor disposed on both sides of blocking capacitor C_(hvm). For example, a first one or more input channels 110 are electrically coupled to a point along the electrical conductor disposed between the PVWG 150 and the blocking capacitor C_(hvm) and a second one or input channel 110 are coupled to a point along the electrical conductor disposed between blocking capacitor C_(hvm) and the biasing electrode 804 in the processing chamber 800.

Pulse Waveform Examples

FIG. 9A illustrates an example of a pulsed voltage waveform 950 that is established at the biasing electrode 804. The pulsed voltage waveform 950 shown in FIG. 9A results in the substrate voltage waveform 951 shown in FIG. 9B, and thus can enable keeping the sheath voltage nearly constant for about 90% of the substrate processing time during a plasma process. The pulsed voltage waveforms 950 and 951 pictured in FIGS. 9A and 9B, are generally based on a waveform that could be generated from the simplified electrical circuit 840 illustrated in FIG. 8B. The waveforms illustrated in FIGS. 9A-9B are only intended to show a simplified schematic representations of a pulsed voltage waveform that can be used with one of the methods described herein, which can be used during plasma processing of a substrate. The actual waveforms generated by the PVWG 150 can be significantly more complex and contain a number of fine-scale features (e.g., high-frequency oscillations caused by the presence of inductive elements) that are not shown in FIGS. 9A-9B. However, examples of some types of fine scale features can be seen in FIGS. 6A-6B and 7A-7B. However, these fine-scale features are not essential for understanding of the underlying physical phenomena determining the general shape of the actual pulsed voltage waveform produced by the pulsed voltage biasing scheme and control methods proposed herein.

In FIG. 9A, the pulsed voltage waveform 950 comprises a periodic series of short positive pulses repeating with a period T (e.g., 2.5 microseconds), on top of a voltage offset. A waveform within each period (repetition cycle) includes the following:

(1) A positive voltage jump to charge the system's stray capacitor and collapse the cathode sheath, i.e., the sheath collapse phase 961, during which the sheath capacitor C_(sh) is discharged and the substrate potential is brought to the level of the local plasma potential (as illustrated in FIG. 9B). The sheath collapse phase 961 enables rapid recharging of the chuck capacitor C_(e) by electrons provided from the plasma during the ESC recharging phase 962. The switch S1 (see FIG. 8B) closes and remains in the closed (On) position for the duration of the phase 961, allowing the nanosecond pulse generator, such as PVWG 150, to maintain a substantially constant positive voltage across its output and supply a current to the system. The duration T1 of the phase 961 is much shorter than the duration T4 of the ion current phase 964 (described below) or than the overall period T, and is typically of the order of several tens of nanoseconds (e.g., 20-50 ns). This is because the plasma current during the phase 961 is carried by electrons—namely, the electron cloud is moving towards the substrate and gradually sweeps over the ion space charge, thus eliminating the sheath voltage drop—and the electron velocity is much greater than the ion velocity, due to a very large mass ratio between the two species.

(2) Recharging of the chuck capacitor C_(e), during the ESC recharging phase 962, by rapidly injecting a charge of equal value and opposite polarity to the total charge accumulated on the substrate surface during the ion current phase 964 (described below). As during the phase 961, the PVWG 150 maintains a substantially constant positive voltage across its output (switch S1 remains in the “On” position). Similarly to the phase 961, the duration T2 of the phase 962 is much shorter than the duration T4 of the ion current phase 964 (described below) or than the overall period T, and is typically of the order of several tens of nanoseconds (e.g., 30-80 ns). This is because the plasma current during the phase 962 is also carried by electrons—namely, in the absence of the cathode sheath, the electrons reach the substrate and build up the surface charge, thus charging the capacitor C_(e).

(3) A negative voltage jump (V_(OUT)) to discharge the processing chamber's stray capacitor, re-form the sheath and set the value of the sheath voltage (V_(SH)) during the sheath formation phase 963. The switch S1 in FIG. 8B opens at the beginning of the sheath formation phase 963 and the inductive elements rapidly (within about 10 nanoseconds, for example) release their stored magnetic energy into the chuck capacitor, C_(e), and the stray capacitor C_(s). Inductive elements may include the internal components of the PVWG 150 (e.g. the internal conductor) represented by the inductance L_(internal), and the external conductor (e.g. the transmission line 806) represented by the inductances L_(interconnect) and L_(external) in circuit 840. During the magnetic energy release, the corresponding current flows through the flyback diode or a different snubber circuit with a similar function of suppressing (or “snubbing”) the possible voltage spikes. We note here, that without the flyback diode (or a different component with a similar function of “snubbing” the possible voltage spikes), the magnetic energy would need to be released through the resistive current-return output stage, resulting in an impractically large negative voltage across R1 (e.g., −20 kV, which is potentially damaging to the internal components of the pulsed bias generator 240) for several nanoseconds, instead of collapsing to near-zero values. After the magnetic energy is released and the current through inductances L_(interconnect) and L_(external) drops to zero (as well as through L_(internal)), it reverses the direction and flows from the plasma and the stray capacitor to ground through the current-return output stage (the flyback diode, being reverse-biased, blocks the current flow through itself), thus discharging the stray capacitor, C_(s), and charging the sheath capacitor, C_(sh), (i.e., re-forming the sheath). The beginning of sheath formation (charging of C_(sh)) can be clearly identified in FIG. 9B as the point, at which the substrate potential starts decreasing below the local plasma potential. Similarly to the phase 961, the duration T3 of the phase 963 is much shorter than the duration T4 of the ion current phase 964 (described below) or than the overall period T, and is typically of the order of 100-300 ns. This is because the plasma current during the phase 963 is likewise carried by electrons—namely, the electron cloud is moving away from the substrate and gradually exposes the ion space charge, thus forming the sheath and producing the sheath voltage drop. We note that (1) T3 is determined primarily by the stray capacitance, as well as the values of the elements (e.g. resistor) comprising the current-return output stage; and (2) the negative voltage jump, V_(OUT), and established sheath voltage, V_(SH), are determined by V_(m) (magnitude of the nanosecond pulse generator output voltage during phases 961-962), and the total pulse width, T_(tot)=T_(rise)+T_(p)=T₁+T₂.

(4) A long (about 85-90% of the cycle duration T) ion current phase 964 with the duration T4, during which the PVWG 150 likewise does not maintain a positive voltage across its output (switch S1 remains in the Off position) and the ion current flows from plasma to ground through the current-return output stage. The ion current causes accumulation of the positive charge on the substrate surface and gradually discharges the sheath and chuck capacitors, slowly decreasing the sheath voltage drop and bringing the substrate potential closer to zero. This results in the voltage droop ΔV_(SH) in the substrate voltage waveform 951 shown in FIG. 9B. The generated sheath voltage droop is why the pulsed voltage waveform 950 needs to move to the next cycle described in (1)-(3) above, during which the PVWG 150 removes the charge accumulated during the ion current phase (or restores the initial ESC charge) and reestablishes the desired sheath voltage V_(SH). Note that the surface charge and sheath voltage droop accumulate whenever there is an electron-repelling cathode sheath and the unbalanced net current (equal to the ion current) from the bulk plasma. This is because the ion current from the bulk plasma is not balanced by the electron current from the bulk plasma, due to the sheath electric field repelling the electrons away from the substrate. Thus, the surface charge accumulation and voltage droop generation also take place during the sheath formation phase 963, during which there is a non-zero sheath voltage drop present right from the beginning.

As can be seen from the (1)-(4) above, the combined duration of the “electron current” phases 961-963 constituting a single voltage pulse of the pulsed voltage waveform (such as the pulsed voltage waveform 950) is about 200-400 ns, which corresponds to the relatively short duty cycle of about 10-15%. The short duty cycle characteristic of the pulsed voltage waveform 950 is a consequence of a large ion-to-electron mass ratio that is typical for all plasmas. Thus, in the pulsed voltage biasing scheme as discussed herein, the PVWG 150 actively interacts with the plasma only during a short portion of each cycle, allowing the cathode sheath to evolve naturally for the rest of the time. By effectively using the fundamental plasma properties, this biasing scheme enables maintaining a nearly constant sheath voltage for up to ˜90% of the processing time, which results in a single peak IEDF (such as IEDF 970 in FIG. 9C). Conversely, in a conventional biasing scheme, an applied RF voltage modulates the cathode sheath throughout the entire RF period, thus unduly varying the sheath voltage drop all of the time and resulting in a dual-peak IEDF.

The pulsed voltage biasing scheme discussed herein enables maintaining a particular substrate voltage waveform, such as the substrate voltage waveform 951 shown in FIG. 9B, which can be described as a periodic series of short positive pulses 971 on top of the negative voltage offset 972. During each pulse (having a total duration of T5=T1+T2+T3), the substrate potential reaches the local plasma potential and the sheath briefly collapses. However, for about 90% of each cycle (having a cycle duration T), the sheath voltage drop remains nearly constant and approximately equal to the absolute value of the most negative substrate potential, V_(SH) (FIG. 9B), which thus determines the mean ion energy at the substrate surface. During the sheath collapse phase 961 of the biasing cycle, the current from the nanosecond pulse generator (e.g., 814) splits between the processing plasma and the stray capacitor C_(s), connected in parallel, approximately according to the ratio C_(SH)/C_(s) and is not very significant. Because of that and because C_(w) is generally very large, the voltage drop accumulating across the wall sheath during phase 961 is relatively small. As a result, the near-wall plasma potential, V_(w), which is equal to the sum of the wall sheath voltage drop and the expectedly small voltage drop across the wall dielectric coating, remains close to zero. Hence, the local (near-substrate) plasma potential, V_(pl), which is equal to the sum of the near-wall plasma potential and the voltage drop across the bulk plasma, is determined primarily by the latter, and it increases slightly above zero. In turn, during the ESC recharging phase 962 there is no electron-repelling cathode sheath and the wall sheath capacitor is being charged to a substantial voltage (e.g. several hundred volts) by the large current pushed through the ESC by the PVWG 150. Due to the increase of the near-wall plasma potential, as well as the presence of a comparably large voltage drop across the bulk plasma (caused by the same large current), the local (near-substrate) plasma potential, V_(pl), as well as the substrate potential V_(sub), experience a substantial increase of up to about ⅓ of the established sheath voltage V_(SH). Finally, during the sheath formation phase 963, the current through the processing plasma is again (as in phase 961) determined by the ratio C_(SH)/C_(s) and is relatively small (also quickly decaying), as well as the resultant voltage drop across the bulk plasma. Therefore, the local (near-substrate) plasma potential remains approximately equal to the near-wall plasma potential, and they both relax to near-zero values closer to the end of the phase 963, as the wall sheath gets discharged primarily by the ion current to the chamber walls. As a result of the local plasma potential perturbation during phases 961-963, the established sheath voltage V_(SH), constitutes only ˜75% of the overall negative jump in the substrate voltage waveform 951 at the end of the phase 963. The negative jump V′_(SH) defines the maximum sheath voltage for given V_(m) and T_(tot) (attainable only with near-infinite C_(w) and near-zero R_(pl)), and it is close to the negative jump in the pulsed voltage waveform 950, or V′_(SH)˜V_(OUT). The latter is because during the phase 963, the chuck capacitor transfers only a small portion (∝C_(SH)/C_(e)<<1) of its initial charge to the sheath, thus maintaining a nearly constant potential difference between the electrode and the substrate. The relationship V_(SH)/V_(OUT)˜0.75−0.8 can be used in practice to estimate V_(SH) from the measured V_(OUT).

As is discussed herein and further below, in one or more of the embodiments of the disclosure provided herein, the feedback loop 100 and method(s) of using the same are provided to detect and adjust the output of the PVWG 150 to achieve pulsed voltage waveforms that have desirable waveform characteristics, such as the pulsed voltage waveform 950 and/or the substrate voltage waveform 951. In addition to the pulse waveform characteristic(s) discussed above that may detected and adjusted, other pulse waveform characteristic(s) may also be detected and adjusted, which, for example, may include the shape or slope of the pulse waveform during one or more of the pulse phases, the period of one or more of the phases (e.g., T1, T2, T3, T4, and T5), and other features of the pulse waveform.

Method Examples

FIG. 10 is a flow chart of method 1000 for processing a pulsed voltage waveform, according to one or more embodiments. At operation 1010, an input pulsed voltage waveform 140 is processed by the components found in an input channel 110 to form an output waveform 144. In one configuration of an input channel 110, an input pulsed voltage waveform is divided using a first divider ratio to generate a first divided voltage waveform. For example, the input channel 110 ₁ acquires an input pulsed voltage waveform 140 _(1B), and the voltage divider 112 of the conditioning circuit 111 _(1B) of the input channel 110 ₁ receives the input pulsed voltage waveform and generates the first divided voltage waveform.

At operation 1020, the divided voltage waveform coming from the voltage divider 112 is low pass filtered to generate a filtered voltage waveform. In one example, the low pass filter 114 of the input channel 110 ₁ receives the first divided voltage waveform from the voltage divider 112 and generates the filtered voltage waveform, which then forms the output waveform 144 _(1B). The operation 1020 may be optional and may be omitted from the method 1000. Moreover, in some embodiments of method 1000, operation 1020 may be performed while operation 1010 is omitted.

After operations 1010 and/or 1020 have been performed, and the output waveform 144 _(1B) has been generated by each input channels 110 ₁, operation 1030 is then performed. At operation 1030, one or more waveform characteristics received from each input channel, such as input channel 110 ₁, and processed by its respective acquisition channel 122 is determined by an algorithm running on the data acquisition controller 123. For example, the acquisition channel 122 ₁ receives an output waveform from the input channel 110 ₁ and algorithm determines one or more waveform characteristics from the output waveform 144 _(1B).

In some embodiments, during operation 1030 the output waveform 144 from each of the input channels 110 is received by a driver (not shown) that is coupled to its respective acquisition channel 122. In one example, the output waveform 144 _(1B) from the input channel 110 ₁ is received by a driver of the acquisition channel 122 ₁. The driver is used to convert the output waveform received from an input channel 110 into a differential signal. In this configuration, the differential signal is then received by an ADC (not shown) coupled to or within the acquisition channel 122. The ADC converts the differential signal from the analog domain to the digital domain and the output digital signal of the ADC is provided to a processor 121 coupled to the acquisition channel 122. The processor of the data acquisition controller 123 determines the one or more waveform characteristics of the output waveform by analyzing the output digital signal provided from the ADC. For example, the processor 121 analyzes an output digital signal to determine one or more of an amplitude, a pulse width, and a DC offset of a pulse within an output waveform 144 received from the input channel 110.

The operation 1030 may additionally include combining measurements received over a period of time from a corresponding input channel. For example, the data acquisition controller 123 may receive “Z” digitized waveforms from the acquisition channel 122 ₁ over a first period, where Z is a whole number that is equal to two or more. The first period may correspond to “M” number of cycles of the input pulsed voltage waveform, where M is a whole number that is equal to one or more. The acquisition channel 122 ₁ may combine the Z output waveforms. For example, the acquisition channel 122 ₁ may average data corresponding to the Z output waveforms.

The operation 1030 may also additionally include the data acquisition controller 123 performing at least one of: 1) transmitting information related to the determined one or more waveform characteristics of a conditioned voltage waveform to a controller (e.g., controller of the feedback processor 125), and 2) transmitting information related to the second digitized voltage waveforms generated by the acquisition channels to a second controller (e.g., controllers 126, 127, 128 or 191).

At operation 1040, one or more control parameters are generated from the one or more waveform characteristics received from one or more input channels 110. For example, the data acquisition controller 123 transmits information corresponding to the one or more waveform characteristics to a feedback processor 125 and the feedback processor 125 generates the one or more control parameters from the one or more waveform characteristics. Referring back to the earlier input channel configuration example, in one example of operation 1040, the processor receives output waveforms from input channels 110 ₁, 110 ₂, and 110 ₃, after the desired operations 1010-1030 have been performed, transmits information corresponding to the one or more waveform characteristics derived from the waveforms received and processed by the acquisition channels 122 ₁, 122 ₂, and 122 ₃, respectively, to the feedback processor 125. The feedback processor 125 may then generate the one or more control parameters from the one or more received waveform characteristics. In one embodiment, the one or more control parameters may include an indication to adjust a DC charge voltage, adjust a pulse width, and adjust an amplitude of a pulse voltage waveform based on a comparison between the received waveform characteristics and target waveform characteristics stored in a memory of the feedback processor 125 or a memory coupled to the feedback processor 125. The stored target waveform characteristics may be waveform characteristics generated by the feedback loop 100 at a prior instant in time, an average of a series of waveform characteristics generated by the feedback loop 100 over a period of time, idealized waveform characteristics (e.g., model based waveform characteristics) that were generated and input into the memory by a user, or waveform characteristics generated by other desirable means.

Alternatively, or additionally, the data acquisition controller 123 may communicate information corresponding to the one or more waveform characteristics to a separate controller (e.g., controller 127, controller 128, controller 191 and/or the processing chamber controller 126) and the separate controller generates the one or more control parameters from the one or more waveform characteristics. Similarly, in one embodiment, the one or more control parameters generated by the controller may include, for example, an indication to adjust a pulse width, and adjust an amplitude of a pulse voltage waveform based on a comparison between the received waveform characteristics and target waveform characteristics stored in the memory of the controller. The stored target waveform characteristics may be waveform characteristics generated by the feedback loop 100 at a prior instant in time, an average of a series of waveform characteristics generated by the feedback loop 100 over a period of time, idealized waveform characteristics (e.g., model based waveform characteristics) that were generated and input into the memory by a user, or waveform characteristics generated by other desirable means.

At operation 1050, the feedback processor 125, or separate controller, transmits the information corresponding to the one or more control parameters to the PVWG 150. Further, in some embodiments, the data acquisition controller 123 may communicate information corresponding to the one or more waveform characteristics to the controller 128 and the controller 128 generates the one or more control parameters based on a comparison of the determined waveform characteristics and the information corresponding to the one or more target waveform characteristics. Therefore, in one embodiment, at operation 1050, the controller 128 transmits the information corresponding to the one or more control parameters to the PVWG 150, and/or another controller.

During operation 1060, an adjusted pulsed voltage waveform is delivered from the PVWG 150 based on the received one or more control parameters. For example, the PVWG 150 generates an adjusted pulsed voltage waveform that is provided to the biasing electrode 804.

At operation 1070, optionally, a plasma processing chamber process variable is separately or additionally adjusted, wherein the plasma processing chamber process variable may include a set point for a chucking power supply. For example, adjusting a set point for a chucking power supply (e.g., the HVM 816) may include increasing or decreasing the chucking voltage output by the chucking power supply. The adjustment of the set point for a chucking power supply will adjust the DC offset of subsequent pulsed voltage waveforms generated by the PVWG 150. The set point for the chucking power supply may be adjusted such that it is a DC voltage between about −5000 V and about 5000 V. In some embodiments, the method 1000 may omit operation 1060.

In some embodiments of method 1000, an adjusted pulsed voltage waveform is serially performed until a pulsed voltage waveform having desirable pulse waveform characteristics (e.g., target waveform characteristics) is achieved. In some embodiments, operations 1010-1050, or operation 1010-1060, are performed a plurality of times until the one or more target waveform characteristics of a pulsed voltage waveform within one waveform cycle are reached. For example, the controller 128, and/or the feedback processor 125 may change the one or more control parameters based on updated waveform characteristics determined by the data acquisition controller 123. The updated waveform characteristics are acquired by continuously processing the input pulsed voltage waveforms acquired by one or more of the input channels 110. In one example, the pulse width and/or amplitude may be increased until the pulse width and/or amplitude reach the corresponding target value that is stored in memory of the feedback processor or memory coupled to or within the data acquisition controller 123. Further, the adjusted pulsed voltage waveform can be continually adjusted, by changing one or more of the control parameters, until a maximum limit of a DC offset voltage is reached. For example, the one or more control parameters may be serially varied until the maximum DC offset voltage is reached.

In some embodiments, establishing the adjusted pulsed voltage waveform comprises changing the one or more of the control parameters until a maximum time limit for algorithm convergence is reached. For example, the feedback processor 125 monitors how long the PVWG 150 takes to generate an adjusted pulsed voltage waveform having one or more of the target waveform characteristics. When the PVWG 150 fails to generate an adjusted pulsed voltage waveform that is able to achieve a target pulsed waveform characteristic within a time limit, the feedback processor 125 may instruct the PVWG 150 to change another waveform characteristic. Additionally or alternatively, establishing the adjusted pulsed voltage waveform comprises changing one or more of the control parameters until a prior determined maximum limit of a pulse width of a pulsed voltage waveform is reached. Further, establishing the adjusted pulsed voltage waveform comprises changing one or more of the control parameters until a minimum limit of pulsed width of a pulsed voltage waveform is reached. The time limit and the maximum limit of a pulse width generally include prior determined values that are stored in memory (e.g., the memory 124, or 126A) and are retrieved by the processor (e.g., feedback processor 125 or the controller 128) for comparison the one or more pulsed voltage waveforms received by one or more of the input channels 110.

FIG. 11 is a flowchart illustrating a method 1100 for controlling a pulsed voltage waveform, according to one or more embodiments. At operation 1110, an output waveform 144 is generated by a first input channel 110. For example, the input channel 110 ₁ acquires an input pulsed voltage waveform 140 _(1B) and generates an output waveform 144 _(1B) from the input pulsed voltage waveform 140 _(1B). The input channel 110 ₁ may include a voltage divider 112 and a low pass filter 114, and generating the first output waveform comprises generating a divided voltage waveform from the input pulsed voltage waveform with the voltage divider 112 and generating a filtered voltage waveform by low pass filtering the voltage divided waveform with the low pass filter 114. In another example, the input channel 110 ₁ omits the low pass filter 114 and generating output waveform comprises generating a divided voltage waveform from the input pulsed voltage waveform with the voltage divider 112.

At operation 1120, a second output waveform is generated by a second input channel 110. For example, the input channel 110 ₂ acquires an input pulsed voltage waveform 140 ₂ and generates an output waveform 144 ₂ from the input pulsed voltage waveform 140 ₂. The input channel 110 ₂ may include a voltage divider 112 and a low pass filter 114 and generating the output waveform 144 ₂ comprises generating a divided voltage waveform from the input pulsed voltage waveform with the voltage divider 112 and generating a filtered voltage waveform by low pass filtering the voltage divided waveform with the low pass filter 114.

At operation 1130, a third output waveform is generated by a third input channel 110. For example, in one embodiment, the input channel 110 ₃ acquires an input pulsed voltage waveform 140 ₃ and generates an output waveform 144 ₃ from the input pulsed voltage waveform 140 ₃. The input channel 110 ₃ may include a low pass filter 114 and generating the output waveform 144 ₃ comprises generating a filtered voltage waveform formed by low pass filtering the input pulsed voltage waveform 140 ₃ by use of the low pass filter 114.

At operation 1140, one or more waveform characteristics are determined. For example, the acquisition channels 122 ₁, 122 ₂ and 122 ₃ receives their respective output waveforms 144 ₁, 144 ₂ and 144 ₃ from the input channel 110, 110 ₂ and 110 ₃ and provide the output waveforms to the data acquisition controller 123 to determine one or more waveform characteristics based on the different types of voltage waveform information received from the output waveforms 144 ₁, 144 ₂ and 144 ₃. In some embodiments, the one or more waveform characteristics determined by the acquisition channel 122 ₁ differs from the one or more waveform characteristics determined by the acquisition channel 122 ₂, and the one or more waveform characteristics determined by the acquisition channel 122 ₃ differ from the one or more waveform characteristics determined by the acquisition channel 122 ₁ and the acquisition channel 122 ₂. Further, in one example, data acquisition controller 123 in combination with the acquisition channel 122 ₁ determines an amplitude (Ampl) and a pulse width W from the corresponding measured waveform, the data acquisition controller 123 in combination with the acquisition channel 122 ₂ determines an ion current offset from the corresponding measured waveform, and the data acquisition controller 123 in combination with the acquisition channel 122 ₃ determines the maximum ion current from the corresponding received output waveforms.

At operation 1150, one or more control parameters are generated from the waveform characteristics determined by the data acquisition controller 123 based on the information received from in the output waveforms 144 ₁, 144 ₂ and 144 ₃. For example, the data acquisition controller 123 transmits information corresponding to the one or more waveform characteristics to a feedback processor 125 (or separate controller) and the feedback processor 125 (or separate controller) generates the one or more control parameters from the one or more determined waveform characteristics. During operation 1150, the feedback processor 125 receives the determined one or more waveform characteristics and then by use of one or more algorithms generates one or more control parameters based on the one or more received waveform characteristics. In one embodiment, the one or more control parameters may include an indication to adjust a DC charge voltage, adjust a pulse width, and adjust an amplitude of a pulse voltage waveform based on a comparison between waveform characteristics received from two or more different input channels and target waveform characteristics stored in a memory of the feedback processor 125 or a memory coupled to the feedback processor 125.

At operation 1160, as similarly discussed above in operation 1050, the feedback processor 125 transmits the information corresponding to the generated control parameters to the PVWG 150.

Further, operation 1170 is generally similar to that of operation 1060, and thus an adjusted pulsed voltage waveform is delivered from the PVWG 150 based on the received one or more control parameters. For example, the PVWG 150 generates an adjusted pulsed voltage waveform that is provided to the biasing electrode 804. Additionally, at operation 1170, a set point for a chucking power supply is also optionally adjusted.

In some embodiments of method 1100, operations 1110-1170 are performed multiple times until an adjusted pulsed voltage waveform having desirable pulse waveform characteristics (e.g., target waveform characteristics) is achieved. In some embodiments, operations 1110-1170 are performed a plurality of times until one or more target waveform characteristics of a pulsed voltage waveform within one waveform cycle are reached.

While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. 

What is claimed is:
 1. A feedback loop for controlling a pulsed voltage waveform comprising a data acquisition system comprising: a first input channel comprising a first conditioning circuit configured to generate a first conditioned voltage waveform from a first input voltage waveform; and a fast data acquisition module comprising: a first acquisition channel that is electrically coupled to the first conditioning circuit of the first input channel, and is configured to generate a first digitized voltage waveform from the first conditioned voltage waveform; and a data acquisition controller configured to determine one or more waveform characteristics of the first conditioned voltage waveform by analyzing the first digitized voltage waveform.
 2. The feedback loop of claim 1, further comprising a feedback processor configured to process information related to the first conditioned voltage waveform processed by the fast data acquisition module.
 3. The feedback loop of claim 2, wherein the feedback processor is one of: an external processor connected to the fast data acquisition module via a data communication interface; an internal processor integrated within the fast data acquisition module; or a controller for a substrate processing chamber connected to the fast data acquisition module via the data communication interface.
 4. The feedback loop of claim 1, wherein the pulsed voltage waveform is established by a pulsed voltage waveform generator electrically coupled to a biasing electrode disposed within a substrate support assembly disposed within a plasma processing chamber.
 5. The feedback loop of claim 4, wherein the pulsed voltage waveform generator is electrically coupled to the biasing electrode through an electrical conductor using a generator coupling assembly, and wherein an input end of the first input channel is electrically coupled to an end of the generator coupling assembly.
 6. The feedback loop of claim 1, further comprising a memory that includes instructions, which when executed by the fast data acquisition module cause the fast data acquisition module to process the first conditioned voltage waveform to determine the one or more waveform characteristics of the first conditioned voltage waveform.
 7. The feedback loop of claim 6, further comprising a feedback processor comprising a memory that includes instructions, which when executed by the feedback processor cause the feedback processor to generate one or more control parameters using the determined one or more waveform characteristics of the first conditioned voltage waveform.
 8. The feedback loop of claim 7, wherein the instructions executed by the feedback processor are further configured to cause the feedback processor to transmit information related to the generated one or more control parameters to a pulsed voltage waveform generator.
 9. The feedback loop of claim 8, wherein the pulsed voltage waveform generator further comprises a memory that includes instructions, which when executed by the pulsed voltage waveform generator cause the pulsed voltage waveform generator to establish an adjusted pulsed voltage waveform based on the generated one or more control parameters.
 10. The feedback loop of claim 9, wherein the first input voltage waveform is an adjusted first input voltage waveform, and the instructions executed by the feedback processor are further configured to cause the feedback processor to generate the one or more control parameters until at least one of: the determined one or more waveform characteristics of the first conditioned voltage waveform have reached their target values or limits; a maximum limit of a DC charge voltage is reached; a maximum power limit is reached; a maximum time limit for algorithm convergence is reached; a maximum limit of a pulse width is reached; and a minimum limit of a pulse width is reached.
 11. The feedback loop of claim 6, wherein the instructions executed by the fast data acquisition module are further configured to cause the fast data acquisition module to at least one of: transmit information related to the determined one or more waveform characteristics of the first conditioned voltage waveform to a first controller; and transmit information related to the first digitized voltage waveform to a second controller.
 12. The feedback loop of claim 11, wherein the first controller is a controller for a substrate processing chamber, and the first controller is further configured to adjust a set point for a chucking power supply for the substrate processing chamber based on the information related to the determined one or more waveform characteristics of the first conditioned voltage waveform.
 13. The feedback loop of claim 1, wherein the first conditioning circuit of the first input channel comprises a first voltage divider.
 14. The feedback loop of claim 13, wherein the first voltage divider comprises a first voltage divider cascade and a second voltage divider cascade.
 15. The feedback loop of claim 14, wherein the first voltage divider cascade has a dividing ratio in a range of about 10 to 1 to about 100 to 1, and the second voltage divider cascade has a dividing ratio in a range of about 20 to 1 to about 120 to
 1. 16. The feedback loop of claim 1, wherein the first conditioning circuit of the first input channel comprises a first low pass filter.
 17. The feedback loop of claim 16, wherein the first low pass filter comprises a first filter cascade and a second filter cascade, and wherein the first low pass filter has a frequency response curve comprising a plateau and a cut-off frequency.
 18. The feedback loop of claim 17, wherein the plateau is between 1 MHz and about 7 MHz, and the cut-off frequency is in a range of about 5 MHz to about 10 MHz.
 19. A feedback loop for controlling a pulsed voltage waveform comprising a data acquisition system comprising: a first input channel comprising a first conditioning circuit configured to generate a first conditioned voltage waveform from a first input voltage waveform; a second input channel comprising a second conditioning circuit configured to generate a second conditioned voltage waveform from a second input voltage waveform; and a fast data acquisition module comprising: a first acquisition channel that is electrically coupled to the first conditioning circuit of the first input channel, and is configured to generate a first digitized voltage waveform from the first conditioned voltage waveform; a second acquisition channel that is electrically coupled to the second conditioning circuit of the second input channel, and is configured to generate a second digitized voltage waveform from the second conditioned voltage waveform; and a data acquisition controller configured to determine one or more waveform characteristics of at least one of the first and the second conditioned voltage waveforms by analyzing at least one of the first and the second digitized voltage waveforms.
 20. The feedback loop of claim 19, wherein the pulsed voltage waveform is established by a pulsed voltage waveform generator electrically coupled to a biasing electrode disposed within a substrate support assembly disposed within a plasma processing chamber.
 21. The feedback loop of claim 20, wherein the pulsed voltage waveform generator is electrically coupled to the biasing electrode through an electrical conductor using a generator coupling assembly, and wherein an input end of the first input channel is electrically coupled to an end of the generator coupling assembly.
 22. The feedback loop of claim 20, wherein the pulsed voltage waveform generator is electrically coupled to the biasing electrode through an electrical conductor using a generator coupling assembly, and an input end of the second input channel is electrically coupled to one of an output of a current monitor and a non-grounded end of a current sense resistor, wherein the current monitor is configured to sense a current flowing in the electrical conductor and the current sense resistor is placed within the pulsed voltage waveform generator.
 23. The feedback loop of claim 19, further comprising a memory that includes instructions, which when executed by the fast data acquisition module cause the fast data acquisition module to process at least one of the first and the second conditioned voltage waveforms to determine the one or more waveform characteristics of at least one of the first and the second conditioned voltage waveforms.
 24. The feedback loop of claim 23, further comprising a feedback processor comprising a memory that includes instructions, which when executed by the feedback processor cause the feedback processor to generate one or more control parameters using the determined one or more waveform characteristics of at least one of the first and the second conditioned voltage waveforms.
 25. The feedback loop of claim 24, wherein the instructions executed by the feedback processor are further configured to cause the feedback processor to transmit information related to the generated one or more control parameters to a pulsed voltage waveform generator.
 26. The feedback loop of claim 25, wherein the pulsed voltage waveform generator further comprises a memory that includes the instructions, which when executed by the pulsed voltage waveform generator cause the pulsed voltage waveform generator to establish an adjusted pulsed voltage waveform based on the generated one or more control parameters.
 27. The feedback loop of claim 26, wherein the first and second input voltage waveforms are adjusted input voltage waveforms, and instructions executed by the feedback processor are further configured to cause the feedback processor to generate the one or more control parameters until at least one of: the determined one or more waveform characteristics of at least one of the first and the second conditioned voltage waveforms have reached their target values or limits; a maximum limit of a DC charge voltage is reached; a maximum power limit is reached; a maximum time limit for algorithm convergence is reached; a maximum limit of a pulse width is reached; and a minimum limit of a pulse width is reached.
 28. The feedback loop of claim 27, wherein the instructions executed by the fast data acquisition module are further configured to cause the fast data acquisition module to do at least one of: transmit information related to the determined one or more waveform characteristics of at least one of the first and the second conditioned voltage waveforms to a first controller; and transmit information related to at least one of the first and the second digitized voltage waveforms to a second controller.
 29. The feedback loop of claim 28, wherein the first controller is a controller for a substrate processing chamber, and the first controller is further configured to adjust a set point for a chucking power supply for the substrate processing chamber based on the information related to the determined one or more waveform characteristics of at least one of the first and the second conditioned voltage waveforms.
 30. The feedback loop of claim 19, wherein at least one of: the first conditioning circuit of the first input channel comprises at least one of a first voltage divider and a first low pass filter; and the second conditioning circuit of the second input channel comprises at least one of a second voltage divider and a second low pass filter.
 31. The feedback loop of claim 19, wherein the first conditioning circuit of the first input channel comprises a first voltage divider; the second conditioning circuit of the second input channel comprises a second voltage divider; and a dividing ratio of the first voltage divider is different from the dividing ratio of the second voltage divider. 